mirror of https://github.com/mpv-player/mpv
4419 lines
162 KiB
XML
4419 lines
162 KiB
XML
<?xml version="1.0" encoding="utf-8"?>
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<!-- synced with 1.32 -->
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<!-- Opiekun: Torinthiel -->
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<!-- INCOMPLETE!!!! -->
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<chapter id="encoding-guide">
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<title>Kodowanie przy użyciu <application>MEncodera</application></title>
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<sect1 id="menc-feat-dvd-mpeg4">
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<title>Rippowanie DVD do wysokiej jakości pliku MPEG-4 ("DivX")</title>
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<para>
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Jednym z często zadawanych pytań jest "Jak zrobić rip najlepszej jakości
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przy danej objętości?". Innym pytaniem jest "Jak zrobić najlepszy możliwy
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rip? Nie ważne jaka będzie objętość, chcę najlepszej jakości."
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</para>
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<para>
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To drugie pytanie jest przynajmniej źle postawione. W końcu, jeśli nie
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przejmujesz się wielkością pliku, mógłbyć po prostu skopiować strumień
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MPEG-2 z DVD. Pewnie, dostaniesz AVI wielkości około 5GB, ale jeśli chcesz
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najlepszej jakości i nie przejmujesz się wielkością to jest to najlepsze
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wyjście.
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</para>
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<para>
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Tak na prawdę, powodem dla którego chcesz przekodować DVD na MPEG-4 jest to,
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że <emphasis role="bold">przejmujesz</emphasis> się wielkością pliku.
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</para>
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<para>
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Ciężko jest pokazać książkowy przepis na tworzenie ripu DVD bardzo wysokiej
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jakości. Trzeba wziąć pod uwagę kilka czynników, i powinieneś rozumieć
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szczegóły albo masz dużą szansę że nie będziesz zadowolony z wyników.
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Poniżej zbadamy niektóre problemy i pokażemy przykład. Zakładamy że używasz
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<systemitem class="library">libavcodec</systemitem> do kodowania obrazu,
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chociaż ta sama teoria działą też przy innych kodekach.
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</para>
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<para>
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Jeśli to wydaje Ci się za dużo, to pewnie powinieneś użyć jednej z wielu
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nakładek dostępnych w
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<ulink url="http://mplayerhq.hu/homepage/design7/projects.html#mencoder_frontends">sekcji MEncodera</ulink>
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naszej strony z powiązanymi projektami.
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W ten sposób, powinno się udać otrzymać ripy wysokiej jakości bez zbyt
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myślenia za dużo, ponieważ te narzędzia są projektowane by podejmować za
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Ciebie mądre decyzje.
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</para>
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<sect2 id="menc-feat-dvd-mpeg4-preparing-encode">
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<title>Przygotowanie do kodowania: Identyfikowanie materiału źródłowego
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i framerate</title>
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<para>
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Zanim w ogóle zaczniesz myśleć o kodowaniu filmu, musisz podjąć kilka
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początkowych kroków.
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</para>
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<para>
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Pierwszym i najważniejszym krokiem przed kodowaniem powinno być
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ustalenie jakim typem filmu się zajmujesz.
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Jeśli Twój film jest z DVD albo telewizji (zwykłej, kablowej czy
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satelitarnej), będzie w jednym z dwóch formatów: NTSC w Ameryce Północnej
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i Japonii, PAL w Europie itp.
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Trzeba sobie jednak zdawać sprawę z tego, że jest to tylko format do
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prezentacji w telewizji, i często <emphasis role="bold">ne</emphasis> jest
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oryginalnym formatem filmu.
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Doświadczenie pokazuje że filmy NTSC są trudniejsze do kodowania, ponieważ
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jest więcej elementów do zidentyfikowania w źródle.
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Żeby zrobić odpowienie kodowanie musisz znać oryginalny format filmu.
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Nieuwzględnienie tego skutkuje wieloma wadami wynikowego pliku, na przykład
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brzydkie artefakty przeplotu i powtórzone albo zagubione klatki.
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Poza tym że są pbrzydkie, artefakty są też szkodliwe dla kodowania:
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Dostaniesz gorszą jakość na jednostkę bitrate.
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</para>
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<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-fps">
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<title>Ustalanie źródłowego framerate</title>
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<para>
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Poniżej jest lista popularnych typów materiału źródłowego, gdzie można je
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najczęściej znaleźć i ich własności:
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</para>
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<itemizedlist>
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<listitem><para>
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<emphasis role="bold">Typowy film</emphasis>: Tworzony do wyświetlania przy
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24fps.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">Film PAL</emphasis>: Nagrywany kamerą video PAL
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z prędkością 50 pól na sekundę.
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Pole składa się tylko z parzystych albo nieparzystych linii klatki.
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Telewizja była projektowana by odświerzać je naprzemiennie, jako tania forma
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analogowej kompresji.
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Ludzkie oko podobno kompensuje ten efekt, ale jeśli zrozumiesz przeplot
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nauczysz się go widzieć też w telewizji i nigdy już nie będziesz z niej
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zadowolony.
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Dwa pola <emphasis role="bold">nie</emphasis> dają pełnej klatki, ponieważ
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są uchwycone co 1/50 sekundy, więc nie pasują do siebie, chyba że nie ma
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ruchu.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">Film NTSC</emphasis>: Nagrany kamerą NTSC z prędkością
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6000/1001 pól na sekundę, albo 60 pól na sekundę w erze przedkolorowej.
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Poza tym podobny do PAL.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">Animacja</emphasis>: Zazwyczaj rysowana przy 24fps,
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ale zdarzają się też z mieszanym framerate.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">Grafika komputerowa (CG)</emphasis>: Może być dowolny
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framerate, ale niektóre są częstsze niż inne; wartości 24 i 30 klatek na
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sekundę są typowe dla NTSC, a 25fps jest typowe dla PAL.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">Stary film</emphasis>: Rozmaite niższe framerate.
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</para></listitem>
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</itemizedlist>
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</sect3>
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<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-material">
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<title>Identyfikowanie materiału źródłowego</title>
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<para>
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Filmy składające się z klatek nazywa się progresywnymi,
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podczas gdy te składające się z niezależnych pól nazywa się
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z przeplotem, albo filmem - chociaż ten drugi termin jest niejasny.
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</para>
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<para>
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Żeby nie było za łatwo, niektóre filmy są kombinacją kilku powyższych typów.
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</para>
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<para>
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Najważniejszą różnicą między tymi formatami, jest to że niektóre są oparte
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na klatkach a inne na polach.
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<emphasis role="bold">Zawsze</emphasis> gdy film jest przygotowywany do
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wyświetlania w telewizji jest przekształcany na format oparty na polach.
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Rozliczne metody którymi się tego dokonuje są wspólnie nazywane "pulldown",
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a niesławne "3:2 telecine" z NTSC jest jednym z jego rodzajów.
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Jeżeli oryginał nie był też oparty na polach (z tą samą prędkością),
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dostajesz film w innym formacie niż oryginał.
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</para>
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<itemizedlist>
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<title>Jest kilka popularnych typów pulldown:</title>
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<listitem><para>
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<emphasis role="bold">pulldown PAL 2:2</emphasis>: Najprzyjemniejszy z nich
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wszystkich.
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Każda klatka jest pokazywana przez czas dwóch pól, poprzez wydobycie
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parzystych i nieparzystych linii i pokazywanie ich na przemian.
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Jeśli oryginalny materiał miał 24fps, ten proces przyspiesza film o 4%.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">pulldown PAL 2:2:2:2:2:2:2:2:2:2:2:3</emphasis>:
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Każda 12ta klatka jest pokazywana przez czas trzech pól zamiast tylko dwóch.
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Dzięki temu nie ma przyspieszenia o 4%, ale proces jest o wiele trudniejszy
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do odtworzenia.
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Zazwyczaj występuje w produkcjach muzycznych, gdzie zmiana prędkości o 4%
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poważnie by uszkodziła muzykę.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">NTSC 3:2 telecine</emphasis>: Klatki są pokazywane na
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przemian przez czas 3ch albo 2ch pól.
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To daje częstotliwość pól 2.5 raza większą niż oryginalna częstotliwość
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klatek. Rezultat jest też lekko zwolniony z 60 pól na sekundę do 60000/1001
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pól na sekundę by utrzymać częstotliwość pól w NTSC.
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</para></listitem>
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<listitem><para>
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<emphasis role="bold">NTSC 2:2 pulldown</emphasis>: Używane do pokazywania
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materiałów 30fps na NTSC.
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Przyjemne, dokładnie jak pulldown 2:2 PAL.
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</para></listitem>
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</itemizedlist>
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<para>
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Są też metody konwersji między filmami PAL i NTSC, ale ten temat
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wykracza poza zakres tego podręcznika.
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Jeśli natkniesz się na taki film, i chcesz go zakodować, to największe
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szanse masz odnajdując kopię w oryginalnym formacie.
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Konwersja między tymi dwoma formatami jest wysoce destrukcyjna i nie może
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zostać czysto odwrócona, więc kodowanie będzie o wiele gorszej jakości jeśli
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jest robione z przekonwertowanego źródła.
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</para>
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<para>
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Gdy film jest zapisywany na DVD, kolejne pary pól są zapisywane jako klatka,
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pomimo tego że nie są przezaczone do wyświetlania razem.
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Standard MPEG-2 używany na DVD i w cyfrowej TV pozwala na zakodowanie
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oryginalnej progresywnej klatki i na przechowanie w nagłówku klatki ilości
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pól przez które ta klatka powinna być pokazana.
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Filmy zrobione przy użyciu tej metody są często określane mianem "miękkiego
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telecine" (soft-telecine), ponieważ proces ten tylko informuje odtwarzacz że
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ma on zastosować pulldown, a nie stosuje go samemu.
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Tak jest o wiele lepiej, ponieważ może to zostać łatwo odwrócone (a tak na
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prawdę zignorowane) przez koder i ponieważ zachowuje możliwie najwyższą
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jakość.
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Niestety, wielu producentów DVD i stacji nadawczych nie stosuje prawidłowych
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technik kodowania ale w zamian produkuje filmy przy użyciu "twardego
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telecine" (hard-telecine), gdzie pola są faktycznie powtórzone
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w zakodowanym MPEG-2.
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</para>
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<para>
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Procedury radzenia sobie z takimi przypadkami będą omówione
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<link linkend="menc-feat-telecine">w dalszej części przewodnika</link>.
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Teraz podamy tylko kilka wskazówek jak identyfikować z jakim typem materiału
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mamy do czynienia.
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</para>
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<itemizedlist>
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<title>Regiony NTSC:</title>
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<listitem><para>
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Jeśli <application>MPlayer</application> wyświetla w trakcie oglądania filmu
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że framerate zostało zmienione na 24000/1001, i nigdy nie powraca, to jest
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to prawie na pewno progresywny materiał na którym zastosowano "miękkie
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telecine".
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</para></listitem>
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<listitem><para>
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Jeśli <application>MPlayer</application> pokazuje że framerate zmienia się
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między 24000/1001 i 30000/1001 i czasami widzisz "grzebienie" to jest kilka
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możliwości.
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<!-- Torinthiel: grzebienie mi najlepiej pasują, ale może jest oficjalne tłumaczenie -->
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Kawałki 24000/1001fps są prawie na pewno progresywne, poddane "miękkiemu
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telecine", ale fragmenty 30000/1001 fps mogą albo być 24000/1001 poddanym
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"twardemu telecine" albo filmem NTCS o 60000/1001 polach na sekundę.
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Używaj tych samych metod co w następnych dwóch przypadkach żeby je odróżnić.
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</para></listitem>
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<listitem><para>
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Jeśli <application>MPlayer</application> nigdy nie pokazuje informacji
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o zmianie framerate i każda klatka z ruchem wygląda jak grzebień, to masz
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film NTSC z 60000/1001 polami na sekundę.
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</para></listitem>
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<listitem><para>
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Jeśli <application>MPlayer</application> nigdy nie pokazuje informacji
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o zmianie framerate i dwie klatki z każdych pięciu mają grzebienie, to film
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jest 24000/1001 fps poddanym "twardemu telecine".
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</para></listitem>
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</itemizedlist>
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<itemizedlist>
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<title>Regiony PAL:</title>
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<listitem><para>
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Jeśli nie widzisz grzebieni, to jest to 2:2 pulldown.
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</para></listitem>
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<listitem><para>
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Jeśli na przemian przez pół sekundy widzisz grzebienie a potem nie, to masz
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2:2:2:2:2:2:2:2:2:2:2:3 pulldown.
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</para></listitem>
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<listitem><para>
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Jeśli zawsze widzisz grzebienie w trakcie ruchu, to film jest filmem PAL
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wyświetlanym z 50 polami na sekundę.
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<!-- Torinthiel: wyświetlanym czy nagranym? -->
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</para></listitem>
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</itemizedlist>
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<note><title>Podpowiedź:</title>
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<para>
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<application>MPlayer</application> może zwolnić odtwarzanie filmu opcją
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-speed albo odtwarzać klatka po klatce.
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Spróbuj użyć opcji <option>-speed</option> 0.2 żeby oglądać film bardzo
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wolno, albo naciskaj wielokrotnie klawisz "<keycap>.</keycap>" żeby
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wyświetlać jedną klatkę na raz. Może to pomóc zidentyfikować wzorzec jeśli
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nie możesz go dostrzec przy pełnej prędkości.
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</para>
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</note>
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</sect3>
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</sect2>
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<sect2 id="menc-feat-dvd-mpeg4-2pass">
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<title>Stały kwantyzator a tryb wieloprzebiegowy</title>
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<para>
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Jest możliwe zakodowanie filmu z szeroką gamą jakości.
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Z nowoczesnymi koderami i odrobiną kompresji przed kodekiem (zmniejszenie
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rozdzielczości i usuwanie szumu), możliwe jest osiągnięcie bardzo dobrej
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jakości przy 700 MB, dla 90-110 minutowego filmu kinowego.
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Dodatkowo tylko najdłuższe filmy nie dają się zakodować na 1400 MB z prawie
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doskonałą jakością.
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</para>
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<para>
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Są trzy podejścia do kodowania video: stały bitrate (CBR),
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stały kwantyzator i tryb wieloprzebiegowy (ABR, uśrednione bitrate).
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</para>
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<para>
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Złożoność klatek filmu, a zatem i ilość bitów potrzebna na ich zakodowanie,
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może się bardzo mocno zmieniać w zależności od sceny.
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Nowoczesne kodery potrafią się dostosowywać do tych zmian i zmieniać
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bitrate.
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Jednak w prostych trybach, takich jak CBR, kodery nie znają zapotrzebowania
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na bitrate w przyszłych scenach, więc nie mogą na długo przekraczać
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wymaganego bitrate.
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Bardziej zaawansowane tryby, takie jak kodowanie wieloprzebiegowe, potrafią
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wziąć pod uwagę statystyki z poprzednich przebiegów; to naprawia wyżej
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wymieniony problem.
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</para>
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<note><title>Uwaga:</title>
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<para>
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Większość kodeków obsługujących kodowanie ABR obsługuje tylko kodowanie
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dwuprzebiegowe, podczas gdy niektóre inne, na przykład
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<systemitem class="library">x264</systemitem> albo
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<systemitem class="library">XviD</systemitem> potrafią wykonywać wiele
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przebiegów, z lekką poprawą jakości po każdym przebiegu. Jednak ta poprawa
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nie jest zauważalna ani mierzalna po około 4tym przebiegu.
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Dlatego też, w tej części, tryb dwuprzebiegowy i wieloprzebiegowy będą
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używane zamiennie.
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</para>
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</note>
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<para>
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W każdym z tych trybów, kodek video (na przykład
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<systemitem class="library">libavcodec</systemitem>)
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dzieli klatkę obrazu na makrobloki 16x16 pikseli i stosuje do każdego z nich
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kwantyzator. Im niższy kwantyzator, tym lepsza jakość i tym wyższe bitrate.
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Metody jakiej koder używa do ustalenia kwantyzatora są różne i można nimi
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sterować. (Jest to straszliwe uproszczenie, ale wystarcza do zrozumienia
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podstaw.)
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</para>
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<para>
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Kiedy podajesz stałe bitrate, kodek koduje usuwając tyle szczegółów ile musi
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i tak mało jak to tylko możliwe żeby pozostać poniżej podanego bitrate.
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Jeśli na prawdę nie obchodzi cię wielkość pliku, możesz użyć CBR i podać
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nieskończone bitrate (W praktyce oznacza to bitrate na tyle wysokie że nie
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stanowi bariery, na przykład 10000Kbit.) Bez żadnego ograniczenia na bitrate
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kodek użyje najniższego możliwego kwantyzatora do każdej klatki (ustalonego
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dla <systemitem class="library">libavcodec</systemitem> opcją
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<option>vqmin</option>, domyślnie 2).
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Gdy tylko podasz bitrate na tyle niskie że kodek musi używać wyższego
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kwantyzatora, to prawie na pewno niszczysz film.
|
|
Żeby tego uniknąć, powinieneś pewnie zmniejszyć rozdzielczość filmu, metodą
|
|
opisaną dalej.
|
|
Ogólnie, jeśli troszczysz się o jakość, powinieneś unikać CBR.
|
|
</para>
|
|
|
|
<para>
|
|
Przy stałym kwantyzatorze, kodek używa na każdym makrobloku tego samego
|
|
kwantyzatora, podanego opcją <option>vqscale</option>
|
|
(w przypadku <systemitem class="library">libavcodec</systemitem>).
|
|
Jeśli chcesz możliwie najlepszy efekt, znów ignorując bitrate, możesz użyć
|
|
<option>vqscale=2</option>. Da to ten sam bitrate i PSNR (peak
|
|
signal-to-noise ratio, szczytowa proporcja sygnału do szumu) co CBR
|
|
z <option>vbitrate</option>=nieskończoność i domyślnym
|
|
<option>vqmin</option>.
|
|
</para>
|
|
|
|
<para>
|
|
Problemem przy stałym kwantyzatorze jest to, że używa podanego kwantyzatora
|
|
niezależnie od tego czy makroblok tego wymaga czy nie. To znaczy że można by
|
|
było zastosować do makrobloku wyższy kwantyzator bez utraty postrzegalnej
|
|
jakości. Dlaczego marnować bity na niepotrzebnie niski kwantyzator?
|
|
Mikroprocesor ma tyle cykli ile jest czasu, ale jest tylko pewna ilość bitów
|
|
na twardym dysku.
|
|
</para>
|
|
|
|
<para>
|
|
Przy kodowaniu dwuprzebiegowym, pierwszy przebieg potraktuje film jak przu
|
|
ustawieniu CBR, ale zachowa informacje o własnościach każdej klatki. Te dane
|
|
są później używane przy drugim przebiegu do podejmowania słusznych decyzji
|
|
o używanym kwantyzatorze. Przy szybkich scenach albo niewielu szczegółach
|
|
pewnie użyje większego kwantyzatora, podczas gdy dla powolnych,
|
|
szczegółowych scen będzie niższy kwantyzator.
|
|
</para>
|
|
|
|
<para>
|
|
Jeśli używasz <option>vqscale=2</option> to marnujesz bity. Jeśli używasz
|
|
<option>vqscale=3</option> to nie dostajesz najlepszej możliwej jakości.
|
|
Załóżmy że zakodowałeś swoje DVD przy <option>vqscale=3</option>
|
|
i dostałeś bitrate 1800Kbit. Jeśli zrobisz dwa przebiegi
|
|
z <option>vbitrate=1800</option> ostateczny wynik będzie miał
|
|
<emphasis role="bold">wyższą jakość</emphasis> przy
|
|
<emphasis role="bold">tym samym bitrate</emphasis>.
|
|
</para>
|
|
|
|
<para>
|
|
Ponieważ jesteś już przekonany że prawidłowym wyborem są dwa przebiegi,
|
|
prawdziwym pytaniem jest jakiego bitrate użyć. Nie ma jednej odpowiedzi.
|
|
Idealnie chcesz wybrać bitrate będący najbliżej równowagi między jakością
|
|
a wielkością pliku. To się zmienia w zależności od filmu.
|
|
</para>
|
|
|
|
<para>
|
|
Jeśli wielkość nie ma znaczenia, dobrym punktem wyjściowym do bardzo
|
|
wysokiej jakości jest około 2000Kbit plus minus 200Kbit.
|
|
Jeśli jest dużo akcji albo szczegółów, albo po prostu masz bardzo wrażliwe
|
|
oko, możesz się zdecydować na 2400 albo 2600.
|
|
Przy niektórych DVD możesz nie zauważyć różnicy przy 1400Kbit. Dobrym
|
|
pomysłem jest poeksperymentowanie z kilkoma scenami i różnymi wartościami
|
|
bitrate żeby nabrać wyczucia.
|
|
</para>
|
|
|
|
<para>
|
|
Jeśli chcesz konkretnej wielkości, musisz jakoś obliczyć bitrare.
|
|
Ale zanim to zrobisz, musisz wiedzieć ile miejsca potrzebujesz na dźwięk,
|
|
więc powinieneś <link linkend="menc-feat-dvd-mpeg4-audio">ściągnąć go</link>
|
|
najpierw.
|
|
Możesz wyliczyć bitrate z następującego równania:
|
|
<systemitem>bitrate = (wielkość_docelowa_w_MBajtach - wielkość_dźwięku_w_MB)
|
|
* 1024 * 1024 / długość_w_sekundach * 8 / 1000</systemitem>
|
|
Na przykład by wcisność dwugodzinny film na płytkę 702MB, z 60MB ścieżki
|
|
dźwiękowej, bitrate video musi być:
|
|
<systemitem>(702 - 60) * 1024 * 1024 / (120*60) * 8 / 1000
|
|
= 740kbps</systemitem>
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-constraints">
|
|
<title>Constraints for efficient encoding</title>
|
|
|
|
<para>
|
|
Due to the nature of MPEG-type compression, there are various
|
|
constraints you should follow for maximal quality.
|
|
MPEG splits the video up into 16x16 squares called macroblocks,
|
|
each composed of 4 8x8 blocks of luma (intensity) information and two
|
|
half-resolution 8x8 chroma (color) blocks (one for red-cyan axis and
|
|
the other for the blue-yellow axis).
|
|
Even if your movie width and height are not multiples of 16, the
|
|
encoder will use enough 16x16 macroblocks to cover the whole picture
|
|
area, and the extra space will go to waste.
|
|
So in the interests of maximizing quality at a fixed filesize, it is
|
|
a bad idea to use dimensions that are not multiples of 16.
|
|
</para>
|
|
|
|
<para>
|
|
Most DVDs also have some degree of black borders at the edges. Leaving
|
|
these in place can hurt quality in several ways.
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>
|
|
MPEG-type compression is also highly dependent on frequency domain
|
|
transformations, in particular the Discrete Cosine Transform (DCT),
|
|
which is similar to the Fourier transform. This sort of encoding is
|
|
efficient for representing patterns and smooth transitions, but it
|
|
has a hard time with sharp edges. In order to encode them it must
|
|
use many more bits, or else an artifact known as ringing will
|
|
appear.
|
|
</para>
|
|
|
|
<para>
|
|
The frequency transform (DCT) takes place separately on each
|
|
macroblock (actually each block), so this problem only applies when
|
|
the sharp edge is inside a block. If your black borders begin
|
|
exactly at multiple-of-16 pixel boundaries, this is not a problem.
|
|
However, the black borders on DVDs rarely come nicely aligned, so
|
|
in practice you will always need to crop to avoid this penalty.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>
|
|
In addition to frequency domain transforms, MPEG-type compression uses
|
|
motion vectors to represent the change from one frame to the next.
|
|
Motion vectors naturally work much less efficiently for new content
|
|
coming in from the edges of the picture, because it is not present in
|
|
the previous frame. As long as the picture extends all the way to the
|
|
edge of the encoded region, motion vectors have no problem with
|
|
content moving out the edges of the picture. However, in the presence
|
|
of black borders, there can be trouble:
|
|
</para>
|
|
|
|
<orderedlist continuation="continues">
|
|
<listitem>
|
|
<para>
|
|
For each macroblock, MPEG-type compression stores a vector
|
|
identifying which part of the previous frame should be copied into
|
|
this macroblock as a base for predicting the next frame. Only the
|
|
remaining differences need to be encoded. If a macroblock spans the
|
|
edge of the picture and contains part of the black border, then
|
|
motion vectors from other parts of the picture will overwrite the
|
|
black border. This means that lots of bits must be spent either
|
|
re-blackening the border that was overwritten, or (more likely) a
|
|
motion vector will not be used at all and all the changes in this
|
|
macroblock will have to be coded explicitly. Either way, encoding
|
|
efficiency is greatly reduced.
|
|
</para>
|
|
|
|
<para>
|
|
Again, this problem only applies if black borders do not line up on
|
|
multiple-of-16 boundaries.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Finally, suppose we have a macroblock in the interior of the
|
|
picture, and an object is moving into this block from near the edge
|
|
of the image. MPEG-type coding cannot say "copy the part that is
|
|
inside the picture but not the black border." So the black border
|
|
will get copied inside too, and lots of bits will have to be spent
|
|
encoding the part of the picture that is supposed to be there.
|
|
</para>
|
|
|
|
<para>
|
|
If the picture runs all the way to the edge of the encoded area,
|
|
MPEG has special optimizations to repeatedly copy the pixels at the
|
|
edge of the picture when a motion vector comes from outside the
|
|
encoded area. This feature becomes useless when the movie has black
|
|
borders. Unlike problems 1 and 2, aligning the borders at multiples
|
|
of 16 does not help here.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem>
|
|
<para>
|
|
Despite the borders being entirely black and never changing, there
|
|
is at least a minimal amount of overhead involved in having more
|
|
macroblocks.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>
|
|
For all of these reasons, it is recommended to fully crop black
|
|
borders. Further, if there is an area of noise/distortion at the edge
|
|
of the picture, cropping this will improve encoding efficiency as
|
|
well. Videophile purists who want to preserve the original as close as
|
|
possible may object to this cropping, but unless you plan to encode at
|
|
constant quantizer, the quality you gain from cropping will
|
|
considerably exceed the amount of information lost at the edges.
|
|
</para>
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-crop">
|
|
<title>Cropping and Scaling</title>
|
|
|
|
<para>
|
|
Recall from the previous section that the final picture size you
|
|
encode should be a multiple of 16 (in both width and height).
|
|
This can be achieved by cropping, scaling, or a combination of both.
|
|
</para>
|
|
|
|
<para>
|
|
When cropping, there are a few guidelines that must be followed to
|
|
avoid damaging your movie.
|
|
The normal YUV format, 4:2:0, stores chroma (color) information
|
|
subsampled, i.e. chroma is only sampled half as often in each
|
|
direction as luma (intensity) information.
|
|
Observe this diagram, where L indicates luma sampling points and C
|
|
chroma.
|
|
</para>
|
|
|
|
<informaltable>
|
|
<?dbhtml table-width="40%" ?>
|
|
<?dbfo table-width="40%" ?>
|
|
<tgroup cols="8" align="center">
|
|
<colspec colnum="1" colname="col1"/>
|
|
<colspec colnum="2" colname="col2"/>
|
|
<colspec colnum="3" colname="col3"/>
|
|
<colspec colnum="4" colname="col4"/>
|
|
<colspec colnum="5" colname="col5"/>
|
|
<colspec colnum="6" colname="col6"/>
|
|
<colspec colnum="7" colname="col7"/>
|
|
<colspec colnum="8" colname="col8"/>
|
|
<spanspec spanname="spa1-2" namest="col1" nameend="col2"/>
|
|
<spanspec spanname="spa3-4" namest="col3" nameend="col4"/>
|
|
<spanspec spanname="spa5-6" namest="col5" nameend="col6"/>
|
|
<spanspec spanname="spa7-8" namest="col7" nameend="col8"/>
|
|
<tbody>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
<row>
|
|
<entry spanname="spa1-2">C</entry>
|
|
<entry spanname="spa3-4">C</entry>
|
|
<entry spanname="spa5-6">C</entry>
|
|
<entry spanname="spa7-8">C</entry>
|
|
</row>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
<row>
|
|
<entry spanname="spa1-2">C</entry>
|
|
<entry spanname="spa3-4">C</entry>
|
|
<entry spanname="spa5-6">C</entry>
|
|
<entry spanname="spa7-8">C</entry>
|
|
</row>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
|
|
<para>
|
|
As you can see, rows and columns of the image naturally come in pairs.
|
|
Thus your crop offsets and dimensions <emphasis>must</emphasis> be
|
|
even numbers.
|
|
If they are not, the chroma will no longer line up correctly with the
|
|
luma.
|
|
In theory, it is possible to crop with odd offsets, but it requires
|
|
resampling the chroma which is potentially a lossy operation and not
|
|
supported by the crop filter.
|
|
</para>
|
|
|
|
<para>
|
|
Further, interlaced video is sampled as follows:
|
|
</para>
|
|
|
|
<informaltable>
|
|
<?dbhtml table-width="80%" ?>
|
|
<?dbfo table-width="80%" ?>
|
|
<tgroup cols="16" align="center">
|
|
<colspec colnum="1" colname="col1"/>
|
|
<colspec colnum="2" colname="col2"/>
|
|
<colspec colnum="3" colname="col3"/>
|
|
<colspec colnum="4" colname="col4"/>
|
|
<colspec colnum="5" colname="col5"/>
|
|
<colspec colnum="6" colname="col6"/>
|
|
<colspec colnum="7" colname="col7"/>
|
|
<colspec colnum="8" colname="col8"/>
|
|
<colspec colnum="9" colname="col9"/>
|
|
<colspec colnum="10" colname="col10"/>
|
|
<colspec colnum="11" colname="col11"/>
|
|
<colspec colnum="12" colname="col12"/>
|
|
<colspec colnum="13" colname="col13"/>
|
|
<colspec colnum="14" colname="col14"/>
|
|
<colspec colnum="15" colname="col15"/>
|
|
<colspec colnum="16" colname="col16"/>
|
|
<spanspec spanname="spa1-2" namest="col1" nameend="col2"/>
|
|
<spanspec spanname="spa3-4" namest="col3" nameend="col4"/>
|
|
<spanspec spanname="spa5-6" namest="col5" nameend="col6"/>
|
|
<spanspec spanname="spa7-8" namest="col7" nameend="col8"/>
|
|
<spanspec spanname="spa9-10" namest="col9" nameend="col10"/>
|
|
<spanspec spanname="spa11-12" namest="col11" nameend="col12"/>
|
|
<spanspec spanname="spa13-14" namest="col13" nameend="col14"/>
|
|
<spanspec spanname="spa15-16" namest="col15" nameend="col16"/>
|
|
<tbody>
|
|
<row>
|
|
<entry namest="col1" nameend="col8">Top field</entry>
|
|
<entry namest="col9" nameend="col16">Bottom field</entry>
|
|
</row>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry spanname="spa1-2">C</entry>
|
|
<entry spanname="spa3-4">C</entry>
|
|
<entry spanname="spa5-6">C</entry>
|
|
<entry spanname="spa7-8">C</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry spanname="spa9-10">C</entry>
|
|
<entry spanname="spa11-12">C</entry>
|
|
<entry spanname="spa13-14">C</entry>
|
|
<entry spanname="spa15-16">C</entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry spanname="spa1-2">C</entry>
|
|
<entry spanname="spa3-4">C</entry>
|
|
<entry spanname="spa5-6">C</entry>
|
|
<entry spanname="spa7-8">C</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
<row>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry spanname="spa9-10">C</entry>
|
|
<entry spanname="spa11-12">C</entry>
|
|
<entry spanname="spa13-14">C</entry>
|
|
<entry spanname="spa15-16">C</entry>
|
|
</row>
|
|
<row>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
<entry>L</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
|
|
<para>
|
|
As you can see, the pattern does not repeat until after 4 lines.
|
|
So for interlaced video, your y-offset and height for cropping must
|
|
be multiples of 4.
|
|
</para>
|
|
|
|
<para>
|
|
Native DVD resolution is 720x480 for NTSC, and 720x576 for PAL, but
|
|
there is an aspect flag that specifies whether it is full-screen (4:3) or
|
|
wide-screen (16:9). Many (if not most) widescreen DVDs are not strictly
|
|
16:9, and will be either 1.85:1 or 2.35:1 (cinescope). This means that
|
|
there will be black bands in the video that will need to be cropped out.
|
|
</para>
|
|
|
|
<para>
|
|
<application>MPlayer</application> provides a crop detection filter that
|
|
will determine the crop rectangle (<option>-vf cropdetect</option>).
|
|
Run <application>MPlayer</application> with
|
|
<option>-vf cropdetect</option> and it will print out the crop
|
|
settings to remove the borders.
|
|
You should let the movie run long enough that the whole picture
|
|
area is used, in order to get accurate crop values.
|
|
</para>
|
|
|
|
<para>
|
|
Then, test the values you get with <application>MPlayer</application>,
|
|
using the command line which was printed by
|
|
<option>cropdetect</option>, and adjust the rectangle as needed.
|
|
The <option>rectangle</option> filter can help by allowing you to
|
|
interactively position the crop rectangle over your movie.
|
|
Remember to follow the above divisibility guidelines so that you
|
|
do not misalign the chroma planes.
|
|
</para>
|
|
|
|
<para>
|
|
In certain cases, scaling may be undesirable.
|
|
Scaling in the vertical direction is difficult with interlaced
|
|
video, and if you wish to preserve the interlacing, you should
|
|
usually refrain from scaling.
|
|
If you will not be scaling but you still want to use multiple-of-16
|
|
dimensions, you will have to overcrop.
|
|
Do not undercrop, since black borders are very bad for encoding!
|
|
</para>
|
|
|
|
<para>
|
|
Because MPEG-4 uses 16x16 macroblocks, you will want to make sure that each
|
|
dimension of the video you are encoding is a multiple of 16 or else you
|
|
will be degrading quality, especially at lower bitrates. You can do this
|
|
by rounding the width and height of the crop rectangle down to the nearest
|
|
multiple of 16.
|
|
As stated earlier, when cropping, you will want to increase the Y offset by
|
|
half the difference of the old and the new height so that the resulting
|
|
video is taken from the center of the frame. And because of the way DVD
|
|
video is sampled, make sure the offset is an even number. (In fact, as a
|
|
rule, never use odd values for any parameter when you are cropping and
|
|
scaling video.) If you are not comfortable throwing a few extra pixels
|
|
away, you might prefer instead to scale the video instead. We will look
|
|
at this in our example below.
|
|
You can actually let the <option>cropdetect</option> filter do all of the
|
|
above for you, as it has an optional <option>round</option> parameter that
|
|
is equal to 16 by default.
|
|
</para>
|
|
|
|
<para>
|
|
Also, be careful about "half black" pixels at the edges. Make sure you
|
|
crop these out too, or else you will be wasting bits there that
|
|
are better spent elsewhere.
|
|
</para>
|
|
|
|
<para>
|
|
After all is said and done, you will probably end up with video whose pixels
|
|
are not quite 1.85:1 or 2.35:1, but rather something close to that. You
|
|
could calculate the new aspect ratio manually, but
|
|
<application>MEncoder</application> offers an option for <systemitem
|
|
class="library">libavcodec</systemitem> called <option>autoaspect</option>
|
|
that will do this for you. Absolutely do not scale this video up in order to
|
|
square the pixels unless you like to waste your hard disk space. Scaling
|
|
should be done on playback, and the player will use the aspect stored in
|
|
the AVI to determine the correct resolution.
|
|
Unfortunately, not all players enforce this auto-scaling information,
|
|
therefore you may still want to rescale.
|
|
</para>
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-resolution-bitrate">
|
|
<title>Choosing resolution and bitrate</title>
|
|
|
|
<para>
|
|
If you will not be encoding in constant quantizer mode, you need to
|
|
select a bitrate.
|
|
The concept of bitrate is quite simple.
|
|
It is the (average) number of bits that will be consumed to store your
|
|
movie, per second.
|
|
Normally bitrate is measured in kilobits (1000 bits) per second.
|
|
The size of your movie on disk is the bitrate times the length of the
|
|
movie in time, plus a small amount of "overhead" (see the section on
|
|
<link linkend="menc-feat-dvd-mpeg4-muxing-avi-limitations">the AVI container</link>
|
|
for instance).
|
|
Other parameters such as scaling, cropping, etc. will
|
|
<emphasis role="bold">not</emphasis> alter the file size unless you
|
|
change the bitrate as well!.
|
|
</para>
|
|
<para>
|
|
Bitrate does <emphasis role="bold">not</emphasis> scale proportionally
|
|
to resolution.
|
|
That is to say, a 320x240 file at 200 kbit/sec will not be the same
|
|
quality as the same movie at 640x480 and 800 kbit/sec!
|
|
There are two reasons for this:
|
|
<orderedlist>
|
|
<listitem><para>
|
|
<emphasis role="bold">Perceptual</emphasis>: You notice MPEG
|
|
artifacts more if they are scaled up bigger!
|
|
Artifacts appear on the scale of blocks (8x8).
|
|
Your eye will not see errors in 4800 small blocks as easily as it
|
|
sees errors in 1200 large blocks (assuming you will be scaling both
|
|
to fullscreen).
|
|
</para></listitem>
|
|
<listitem><para>
|
|
<emphasis role="bold">Theoretical</emphasis>: When you scale down
|
|
an image but still use the same size (8x8) blocks for the frequency
|
|
space transform, you move more data to the high frequency bands.
|
|
Roughly speaking, each pixel contains more of the detail than it
|
|
did before.
|
|
So even though your scaled-down picture contains 1/4 the information
|
|
in the spacial directions, it could still contain a large portion
|
|
of the information in the frequency domain (assuming that the high
|
|
frequencies were underutilized in the original 640x480 image).
|
|
</para></listitem>
|
|
</orderedlist>
|
|
</para>
|
|
<para>
|
|
Past guides have recommended choosing a bitrate and resolution based
|
|
on a "bits per pixel" approach, but this is usually not valid due to
|
|
the above reasons.
|
|
A better estimate seems to be that bitrates scale proportional to the
|
|
square root of resolution, so that 320x240 and 400 kbit/sec would be
|
|
comparable to 640x480 at 800 kbit/sec.
|
|
However this has not been verified with theoretical or empirical
|
|
rigor.
|
|
Further, given that movies vary greatly with regard to noise, detail,
|
|
degree of motion, etc., it is futile to make general recommendations
|
|
for bits per length-of-diagonal (the analog of bits per pixel,
|
|
using the square root).
|
|
</para>
|
|
<para>
|
|
So far we have discussed the difficulty of choosing a bitrate and
|
|
resolution.
|
|
</para>
|
|
|
|
|
|
<sect3 id="menc-feat-dvd-mpeg4-resolution-bitrate-compute">
|
|
<title>Computing the resolution</title>
|
|
<para>
|
|
First, you should compute the encoded aspect ratio:
|
|
<systemitem>ARc = (Wc x (ARa / PRdvd )) / Hc</systemitem>
|
|
<itemizedlist>
|
|
<title>where:</title>
|
|
<listitem><para>
|
|
Wc and Hc are the width and height of the cropped video,
|
|
</para></listitem>
|
|
<listitem><para>
|
|
ARa is the displayed aspect ratio, which usually is 4/3 or 16/9,
|
|
</para></listitem>
|
|
<listitem><para>
|
|
PRdvd is the pixel ratio of the DVD which is equal to 1.25=(720/576) for PAL
|
|
DVDs and 1.5=(720/480) for NTSC DVDs,
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</para>
|
|
|
|
<para>
|
|
Then, you can compute the X and Y resolution, according to a certain
|
|
Compression Quality (CQ) factor:
|
|
<systemitem>ResY = INT(SQRT( 1000*Bitrate/25/ARc/CQ )/16) * 16</systemitem>
|
|
and
|
|
<systemitem>ResX = INT( ResY * ARc / 16) * 16</systemitem>
|
|
</para>
|
|
|
|
<para>
|
|
Okay, but what is the CQ?
|
|
The CQ represents the number of bits per pixel and per frame of the encode.
|
|
Roughly speaking, the greater the CQ, the less the likelihood to see
|
|
encoding artifacts.
|
|
However, if you have a target size for your movie (1 or 2 CDs for instance),
|
|
there is a limited total number of bits that you can spend; therefore it is
|
|
necessary to find a good tradeoff between compressibility and quality.
|
|
</para>
|
|
|
|
<para>
|
|
The CQ depends both on the bitrate and the movie resolution.
|
|
In order to raise the CQ, typically you would downscale the movie given that the
|
|
bitrate is computed in function of the target size and the length of the
|
|
movie, which are constant.
|
|
A CQ below 0.18 usually ends up in a very blocky picture, because there
|
|
are not enough bits to code the information of each macroblock (MPEG4, like
|
|
many other codecs, groups pixels by blocks of several pixels to compress the
|
|
image; if there are not enough bits, the edges of those blocks are
|
|
visible).
|
|
It is therefore wise to take a CQ ranging from 0.20 to 0.22 for a 1 CD rip,
|
|
and 0.26-0.28 for 2 CDs.
|
|
</para>
|
|
|
|
<para>
|
|
Please take note that the CQ is just an indicative figure, as depending on
|
|
the encoded content, a CQ of 0.18 may look just fine for a Bergman, contrary
|
|
to a movie such as The Matrix, which contains many high-motion scenes.
|
|
On the other hand, it is worthless to raise CQ higher than 0.30 as you would
|
|
be wasting bits without any noticeable quality gain.
|
|
</para>
|
|
</sect3>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-filtering">
|
|
<title>Filtering</title>
|
|
|
|
<para>
|
|
Learning how to use <application>MEncoder</application>'s video filters
|
|
is essential to producing good encodes.
|
|
All video processing is performed through the filters -- cropping,
|
|
scaling, color adjustment, noise removal, sharpening, deinterlacing,
|
|
telecine, inverse telecine, and deblocking, just to name a few.
|
|
Along with the vast number of supported input formats, the variety of
|
|
filters available in <application>MEncoder</application> is one of its
|
|
main advantages over other similar programs.
|
|
</para>
|
|
|
|
<para>
|
|
Filters are loaded in a chain using the -vf option:
|
|
|
|
<screen>-vf filter1=options,filter2=options,...</screen>
|
|
|
|
Most filters take several numeric options separated by colons, but
|
|
the syntax for options varies from filter to filter, so read the man
|
|
page for details on the filters you wish to use.
|
|
</para>
|
|
|
|
<para>
|
|
Filters operate on the video in the order they are loaded.
|
|
For example, the following chain:
|
|
|
|
<screen>-vf crop=688:464:12:4,scale=640:464</screen>
|
|
|
|
will first crop the 688x464 region of the picture with upper-left
|
|
corner at (12,4), and then scale the result down to 640x464.
|
|
</para>
|
|
|
|
<para>
|
|
Certain filters need to be loaded at or near the beginning of the
|
|
filter chain, in order to take advantage of information from the
|
|
video decoder that will be lost or invalidated by other filters.
|
|
The principal examples are <option>pp</option> (postprocessing, only
|
|
when it is performing deblock or dering operations),
|
|
<option>spp</option> (another postprocessor to remove MPEG artifacts),
|
|
<option>pullup</option> (inverse telecine), and
|
|
<option>softpulldown</option> (for converting soft telecine to hard
|
|
telecine).
|
|
</para>
|
|
|
|
<para>
|
|
In general, you want to do as little filtering as possible to the movie
|
|
in order to remain close to the original DVD source. Cropping is often
|
|
necessary (as described above), but avoid to scale the video. Although
|
|
scaling down is sometimes preferred to using higher quantizers, we want
|
|
to avoid both these things: remember that we decided from the start to
|
|
trade bits for quality.
|
|
</para>
|
|
|
|
<para>
|
|
Also, do not adjust gamma, contrast, brightness, etc. What looks good
|
|
on your display may not look good on others. These adjustments should
|
|
be done on playback only.
|
|
</para>
|
|
|
|
<para>
|
|
One thing you might want to do, however, is pass the video through a
|
|
very light denoise filter, such as <option>-vf hqdn3d=2:1:2</option>.
|
|
Again, it is a matter of putting those bits to better use: why waste them
|
|
encoding noise when you can just add that noise back in during playback?
|
|
Increasing the parameters for <option>hqdn3d</option> will further
|
|
improve compressibility, but if you increase the values too much, you
|
|
risk degrading the image visibily. The suggested values above
|
|
(<option>2:1:2</option>) are quite conservative; you should feel free to
|
|
experiment with higher values and observe the results for yourself.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-interlacing">
|
|
<title>Interlacing and Telecine</title>
|
|
|
|
<para>
|
|
Almost all movies are shot at 24 fps. Because NTSC is 30000/1001 fps, some
|
|
processing must be done to this 24 fps video to make it run at the correct
|
|
NTSC framerate. The process is called 3:2 pulldown, commonly referred to
|
|
as telecine (because pulldown is often applied during the telecine
|
|
process), and, naively described, it works by slowing the film down to
|
|
24000/1001 fps, and repeating every fourth frame.
|
|
</para>
|
|
|
|
<para>
|
|
No special processing, however, is done to the video for PAL DVDs, which
|
|
run at 25 fps. (Technically, PAL can be telecined, called 2:2 pulldown,
|
|
but this does not become an issue in practice.) The 24 fps film is simply
|
|
played back at 25 fps. The result is that the movie runs slightly faster,
|
|
but unless you are an alien, you probably will not notice the difference.
|
|
Most PAL DVDs have pitch-corrected audio, so when they are played back at
|
|
25 fps things will sound right, even though the audio track (and hence the
|
|
whole movie) has a running time that is 4% less than NTSC DVDs.
|
|
</para>
|
|
|
|
<para>
|
|
Because the video in a PAL DVD has not been altered, you need not worry
|
|
much about framerate. The source is 25 fps, and your rip will be 25
|
|
fps. However, if you are ripping an NTSC DVD movie, you may need to
|
|
apply inverse telecine.
|
|
</para>
|
|
|
|
<para>
|
|
For movies shot at 24 fps, the video on the NTSC DVD is either telecined
|
|
30000/1001, or else it is progressive 24000/1001 fps and intended to be telecined
|
|
on-the-fly by a DVD player. On the other hand, TV series are usually
|
|
only interlaced, not telecined. This is not a hard rule: some TV series
|
|
are interlaced (such as Buffy the Vampire Slayer) whereas some are a
|
|
mixture of progressive and interlaced (such as Angel, or 24).
|
|
</para>
|
|
|
|
<para>
|
|
It is highly recommended that you read the section on
|
|
<link linkend="menc-feat-telecine">How to deal with telecine and interlacing in NTSC DVDs</link>
|
|
to learn how to handle the different possibilities.
|
|
</para>
|
|
|
|
<para>
|
|
However, if you are mostly just ripping movies, likely you are either
|
|
dealing with 24 fps progressive or telecined video, in which case you can
|
|
use the <option>pullup</option> filter <option>-vf
|
|
pullup,softskip</option>.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-encoding-interlaced">
|
|
<title>Encoding interlaced video</title>
|
|
|
|
<para>
|
|
If the movie you want to encode is interlaced (NTSC video or
|
|
PAL video), you will need to choose whether you want to
|
|
deinterlace or not.
|
|
While deinterlacing will make your movie usable on progressive
|
|
scan displays such a computer monitors and projectors, it comes
|
|
at a cost: The fieldrate of 50 or 60000/1001 fields per second
|
|
is halved to 25 or 30000/1001 frames per second, and roughly half of
|
|
the information in your movie will be lost during scenes with
|
|
significant motion.
|
|
</para>
|
|
|
|
<para>
|
|
Therefore, if you are encoding for high quality archival purposes,
|
|
it is recommended not to deinterlace.
|
|
You can always deinterlace the movie at playback time when
|
|
displaying it on progressive scan devices, and future players will
|
|
be able to deinterlace to full fieldrate, interpolating 50 or
|
|
60000/1001 entire frames per second from the interlaced video.
|
|
</para>
|
|
|
|
<para>
|
|
Special care must be taken when working with interlaced video:
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>
|
|
Crop height and y-offset must be multiples of 4.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Any vertical scaling must be performed in interlaced mode.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Postprocessing and denoising filters may not work as expected
|
|
unless you take special care to operate them a field at a time,
|
|
and they may damage the video if used incorrectly.
|
|
</para></listitem>
|
|
</orderedlist>
|
|
|
|
<para>
|
|
With these things in mind, here is our first example:
|
|
</para>
|
|
<screen>
|
|
mencoder <replaceable>capture.avi</replaceable> -mc 0 -oac lavc -ovc lavc -lavcopts \
|
|
vcodec=mpeg2video:vbitrate=6000:ilme:ildct:acodec=mp2:abitrate=224
|
|
</screen>
|
|
<para>
|
|
Note the <option>ilme</option> and <option>ildct</option> options.
|
|
</para>
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-av-sync">
|
|
<title>Notes on Audio/Video synchronization</title>
|
|
<para>
|
|
<application>MEncoder</application>'s audio/video synchronization
|
|
algorithms were designed with the intention of recovering files with
|
|
broken sync.
|
|
However, in some cases they can cause unnecessary skipping and duplication of
|
|
frames, and possibly slight A/V desync, when used with proper input
|
|
(of course, A/V sync issues apply only if you process or copy the
|
|
audio track while transcoding the video, which is strongly encouraged).
|
|
Therefore, you may have to switch to basic A/V sync with
|
|
the <option>-mc 0</option> option, or put this in your
|
|
<systemitem>~/.mplayer/mencoder</systemitem> config file, as long as
|
|
you are only working with good sources (DVD, TV capture, high quality
|
|
MPEG-4 rips, etc) and not broken ASF/RM/MOV files.
|
|
</para>
|
|
<para>
|
|
If you want to further guard against strange frame skips and
|
|
duplication, you can use both <option>-mc 0</option> and
|
|
<option>-noskip</option>.
|
|
This will prevent <emphasis>all</emphasis> A/V sync, and copy frames
|
|
one-to-one, so you cannot use it if you will be using any filters that
|
|
unpredictably add or drop frames, or if your input file has variable
|
|
framerate!
|
|
Therefore, using <option>-noskip</option> is not in general recommended.
|
|
</para>
|
|
<para>
|
|
The so-called "three-pass" audio encoding which <application>MEncoder</application>
|
|
supports has been reported to cause A/V desync.
|
|
This will definitely happen if it is used in conjunction with certain
|
|
filters, therefore, it is now recommended <emphasis>not</emphasis> to
|
|
use three-pass audio mode.
|
|
This feature is only left for compatibility purposes and for expert
|
|
users who understand when it is safe to use and when it is not.
|
|
If you have never heard of three-pass mode before, forget that we
|
|
even mentioned it!
|
|
</para>
|
|
<para>
|
|
There have also been reports of A/V desync when encoding from stdin
|
|
with <application>MEncoder</application>.
|
|
Do not do this! Always use a file or CD/DVD/etc device as input.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-audio">
|
|
<title>Audio</title>
|
|
|
|
<para>
|
|
Audio is a much simpler problem to solve: if you care about quality, just
|
|
leave it as is.
|
|
Even AC3 5.1 streams are at most 448Kbit/s, and they are worth every bit.
|
|
You might be tempted to transcode the audio to high quality Vorbis, but
|
|
just because you do not have an A/V receiver for AC3 pass-through today
|
|
does not mean you will not have one tomorrow. Future-proof your DVD rips by
|
|
preserving the AC3 stream.
|
|
You can keep the AC3 stream either by copying it directly into the video
|
|
stream <link linkend="menc-feat-mpeg4">during the encoding</link>.
|
|
You can also extract the AC3 stream in order to mux it into containers such
|
|
as NUT or Matroska.
|
|
<screen>mplayer <replaceable>source_file.vob</replaceable> -aid 129 -dumpaudio -dumpfile <replaceable>sound.ac3</replaceable></screen>
|
|
will dump into the file <replaceable>sound.ac3</replaceable> the
|
|
audio track number 129 from the file
|
|
<replaceable>source_file.vob</replaceable> (NB: DVD VOB files
|
|
usually use a different audio numbering,
|
|
which means that the VOB audio track 129 is the 2nd audio track of the file).
|
|
</para>
|
|
|
|
<para>
|
|
But sometimes you truly have no choice but to further compress the
|
|
sound so that more bits can be spent on the video.
|
|
Most people choose to compress audio with either MP3 or Vorbis audio
|
|
codecs.
|
|
While the latter is a very space-efficient codec, MP3 is better supported
|
|
by hardware players, although this trend is changing.
|
|
</para>
|
|
|
|
<para>
|
|
Do <emphasis>not</emphasis> use <option>-nosound</option> when encoding
|
|
a file with audio, even if you will be encoding and muxing audio
|
|
separately later.
|
|
Though it may work in ideal cases, using <option>-nosound</option> is
|
|
likely to hide some problems in your encoding command line setting.
|
|
In other words, having a soundtrack during your encode assures you that,
|
|
provided you do not see messages such as
|
|
<quote>Too many audio packets in the buffer</quote>, you will be able
|
|
to get proper sync.
|
|
</para>
|
|
|
|
<para>
|
|
You need to have <application>MEncoder</application> process the sound.
|
|
You can for example copy the orignal soundtrack during the encode with
|
|
<option>-oac copy</option> or convert it to a "light" 4 kHz mono WAV
|
|
PCM with <option>-oac pcm -channels 1 -srate 4000</option>.
|
|
Otherwise, in some cases, it will generate a video file that will not sync
|
|
with the audio.
|
|
Such cases are when the number of video frames in the source file does
|
|
not match up to the total length of audio frames or whenever there
|
|
are discontinuities/splices where there are missing or extra audio frames.
|
|
The correct way to handle this kind of problem is to insert silence or
|
|
cut audio at these points.
|
|
However <application>MPlayer</application> cannot do that, so if you
|
|
demux the AC3 audio and encode it with a separate app (or dump it to PCM with
|
|
<application>MPlayer</application>), the splices will be left incorrect
|
|
and the only way to correct them is to drop/dup video frames at the
|
|
splice.
|
|
As long as <application>MEncoder</application> sees the audio when it is
|
|
encoding the video, it can do this dropping/duping (which is usually OK
|
|
since it takes place at full black/scenechange, but if
|
|
<application>MEncoder</application> cannot see the audio, it will just
|
|
process all frames as-is and they will not fit the final audio stream when
|
|
you for example merge your audio and video track into a Matroska file.
|
|
</para>
|
|
|
|
<para>
|
|
First of all, you will have to convert the DVD sound into a WAV file that the
|
|
audio codec can use as input.
|
|
For example:
|
|
<screen>mplayer <replaceable>source_file.vob</replaceable> -ao pcm:file=<replaceable>destination_sound.wav</replaceable> -vc dummy -aid 1 -vo null</screen>
|
|
will dump the second audio track from the file
|
|
<replaceable>source_file.vob</replaceable> into the file
|
|
<replaceable>destination_sound.wav</replaceable>.
|
|
You may want to normalize the sound before encoding, as DVD audio tracks
|
|
are commonly recorded at low volumes.
|
|
You can use the tool <application>normalize</application> for instance,
|
|
which is available in most distributions.
|
|
If you are using Windows, a tool such as <application>BeSweet</application>
|
|
can do the same job.
|
|
You will compress in either Vorbis or MP3.
|
|
For example:
|
|
<screen>oggenc -q1 <replaceable>destination_sound.wav</replaceable></screen>
|
|
will encode <replaceable>destination_sound.wav</replaceable> with
|
|
the encoding quality 1, which is roughly equivalent to 80Kb/s, and
|
|
is the minimum quality at which you should encode if you care about
|
|
quality.
|
|
Please note that MEncoder currently cannot mux Vorbis audio tracks
|
|
into the output file because it only supports AVI and MPEG
|
|
containers as an output, each of which may lead to audio/video
|
|
playback synchronization problems with some players when the AVI file
|
|
contain VBR audio streams such as Vorbis.
|
|
Do not worry, this document will show you how you can do that with third
|
|
party programs.
|
|
</para>
|
|
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-muxing">
|
|
<title>Muxing</title>
|
|
<para>
|
|
Now that you have encoded your video, you will most likely want
|
|
to mux it with one or more audio tracks into a movie container, such
|
|
as AVI, MPEG, Matroska or NUT.
|
|
<application>MEncoder</application> is currently only able to natively output
|
|
audio and video into MPEG and AVI container formats.
|
|
for example:
|
|
<screen>mencoder -oac copy -ovc copy -o <replaceable>output_movie.avi</replaceable> -audiofile <replaceable>input_audio.mp2</replaceable> <replaceable>input_video.avi</replaceable></screen>
|
|
This would merge the video file <replaceable>input_video.avi</replaceable>
|
|
and the audio file <replaceable>input_audio.mp2</replaceable>
|
|
into the AVI file <replaceable>output_movie.avi</replaceable>.
|
|
This command works with MPEG-1 layer I, II and III (more commonly known
|
|
as MP3) audio, WAV and a few other audio formats too.
|
|
</para>
|
|
|
|
<para>
|
|
MEncoder features experimental support for
|
|
<systemitem class="library">libavformat</systemitem>, which is a
|
|
library from the FFmpeg project that supports muxing and demuxing
|
|
a variety of containers.
|
|
For example:
|
|
<screen>mencoder -oac copy -ovc copy -o <replaceable>output_movie.asf</replaceable> -audiofile <replaceable>input_audio.mp2</replaceable> <replaceable>input_video.avi</replaceable> -of lavf -lavfopts format=asf</screen>
|
|
This will do the same thing as the previous example, except that
|
|
the output container will be ASF.
|
|
Please note that this support is highly experimental (but getting
|
|
better every day), and will only work if you compiled
|
|
<application>MPlayer</application> with the support for
|
|
<systemitem class="library">libavformat</systemitem> enabled (which
|
|
means that a pre-packaged binary version will not work in most cases).
|
|
</para>
|
|
|
|
|
|
<sect3 id="menc-feat-dvd-mpeg4-muxing-filter-issues">
|
|
<title>Improving muxing and A/V sync reliability</title>
|
|
<para>
|
|
You may experience some serious A/V sync problems while trying to mux
|
|
your video and some audio tracks, where no matter how you adjust the
|
|
audio delay, you will never get proper sync.
|
|
That may happen when you use some video filters that will drop or
|
|
duplicate some frames, like the inverse telecine filters.
|
|
It is strongly encouraged to append the <option>harddup</option> video
|
|
filter at the end of the filter chain to avoid this kind of problem.
|
|
</para>
|
|
|
|
<para>
|
|
Without <option>harddup</option>, if <application>MEncoder</application>
|
|
wants to duplicate a frame, it relies on the muxer to put a mark on the
|
|
container so that the last frame will be displayed again to maintain
|
|
sync while writing no actual frame.
|
|
With <option>harddup</option>, <application>MEncoder</application>
|
|
will instead just push the last frame displayed again into the filter
|
|
chain.
|
|
This means that the encoder receives the <emphasis>exact</emphasis>
|
|
same frame twice, and compresses it.
|
|
This will result in a slightly bigger file, but will not cause problems
|
|
when demuxing or remuxing into other container formats.
|
|
</para>
|
|
|
|
<para>
|
|
You may also have no choice but to use <option>harddup</option> with
|
|
container formats that are not too tightly linked with
|
|
<application>MEncoder</application> such as the ones supported through
|
|
<systemitem class="library">libavformat</systemitem>, which may not
|
|
support frame duplication at the container level.
|
|
</para>
|
|
</sect3>
|
|
|
|
|
|
<sect3 id="menc-feat-dvd-mpeg4-muxing-avi-limitations">
|
|
<title>Limitations of the AVI container</title>
|
|
<para>
|
|
Although it is the most widely-supported container format after MPEG-1,
|
|
AVI also has some major drawbacks.
|
|
Perhaps the most obvious is the overhead.
|
|
For each chunk of the AVI file, 24 bytes are wasted on headers and
|
|
index.
|
|
This translates into a little over 5 MB per hour, or 1-2.5%
|
|
overhead for a 700 MB movie. This may not seem like much, but it could
|
|
mean the difference between being able to use 700 kbit/sec video or
|
|
714 kbit/sec, and every bit of quality counts.
|
|
</para>
|
|
|
|
<para>
|
|
In addition this gross inefficiency, AVI also has the following major
|
|
limitations:
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem>
|
|
<para>
|
|
Only fixed-fps content can be stored. This is particularly limiting
|
|
if the original material you want to encode is mixed content, for
|
|
example a mix of NTSC video and film material.
|
|
Actually there are hacks that can be used to store mixed-framerate
|
|
content in AVI, but they increase the (already huge) overhead
|
|
fivefold or more and so are not practical.
|
|
</para>
|
|
</listitem>
|
|
<listitem>
|
|
<para>
|
|
Audio in AVI files must be either constant-bitrate (CBR) or
|
|
constant-framesize (i.e. all frames decode to the same number of
|
|
samples).
|
|
Unfortunately, the most efficient codec, Vorbis, does not meet
|
|
either of these requirements.
|
|
Therefore, if you plan to store your movie in AVI, you will have to
|
|
use a less efficient codec such as MP3 or AC3.
|
|
</para>
|
|
</listitem>
|
|
</orderedlist>
|
|
|
|
<para>
|
|
Having said all that, <application>MEncoder</application> does not
|
|
currently support variable-fps output or Vorbis encoding.
|
|
Therefore, you may not see these as limitations if
|
|
<application>MEncoder</application> is the
|
|
only tool you will be using to produce your encodes.
|
|
However, it is possible to use <application>MEncoder</application>
|
|
only for video encoding, and then use external tools to encode
|
|
audio and mux it into another container format.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-dvd-mpeg4-muxing-matroska">
|
|
<title>Muxing into the Matroska container</title>
|
|
<para>
|
|
Matroska is a free, open standard container format, aiming
|
|
to offer a lot of advanced features, which older containers
|
|
like AVI cannot handle.
|
|
For example, Matroska supports variable bitrate audio content
|
|
(VBR), variable framerates (VFR), chapters, file attachments,
|
|
error detection code (EDC) and modern A/V Codecs like "Advanced Audio
|
|
Coding" (AAC), "Vorbis" or "MPEG-4 AVC" (H.264), next to nothing
|
|
handled by AVI.
|
|
</para>
|
|
|
|
<para>
|
|
The tools required to create Matroska files are collectively called
|
|
<application>mkvtoolnix</application>, and are available for most
|
|
Unix platforms as well as <application>Windows</application>.
|
|
Because Matroska is an open standard you may find other
|
|
tools that suit you better, but since mkvtoolnix is the most
|
|
common, and is supported by the Matroska team itself, we will
|
|
only cover its usage.
|
|
</para>
|
|
|
|
<para>
|
|
Probably the easiest way to get started with Matroska is to use
|
|
<application>MMG</application>, the graphical frontend shipped with
|
|
<application>mkvtoolnix</application>, and follow the
|
|
<ulink url="http://www.bunkus.org/videotools/mkvtoolnix/doc/mkvmerge-gui.html">guide to mkvmerge GUI (mmg)</ulink>
|
|
</para>
|
|
|
|
<para>
|
|
You may also mux audio and video files using the command line:
|
|
<screen>mkvmerge -o <replaceable>output.mkv</replaceable> <replaceable>input_video.avi</replaceable> <replaceable>input_audio1.mp3</replaceable> <replaceable>input_audio2.ac3</replaceable></screen>
|
|
This would merge the video file <replaceable>input_video.avi</replaceable>
|
|
and the two audio files <replaceable>input_audio1.mp3</replaceable>
|
|
and <replaceable>input_audio2.ac3</replaceable> into the Matroska
|
|
file <replaceable>output.mkv</replaceable>.
|
|
Matroska, as mentioned earlier, is able to do much more than that, like
|
|
multiple audio tracks (including fine-tuning of audio/video
|
|
synchronization), chapters, subtitles, splitting, etc...
|
|
Please refer to the documentation of those applications for
|
|
more details.
|
|
</para>
|
|
|
|
</sect3>
|
|
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="menc-feat-telecine">
|
|
<title>How to deal with telecine and interlacing within NTSC DVDs</title>
|
|
|
|
<sect2 id="menc-feat-telecine-intro">
|
|
<title>Introduction</title>
|
|
<formalpara>
|
|
<title>What is telecine?</title>
|
|
<para>
|
|
I suggest you visit this page if you do not understand much of what
|
|
is written in this document:
|
|
<ulink url="http://www.divx.com/support/guides/guide.php?gid=10">http://www.divx.com/support/guides/guide.php?gid=10</ulink>
|
|
This URL links to an understandable and reasonably comprehensive
|
|
description of what telecine is.
|
|
</para></formalpara>
|
|
|
|
<formalpara>
|
|
<title>A note about the numbers.</title>
|
|
<para>
|
|
Many documents, including the guide linked above, refer to the fields
|
|
per second value of NTSC video as 59.94 and the corresponding frames
|
|
per second values as 29.97 (for telecined and interlaced) and 23.976
|
|
(for progressive). For simplicity, some documents even round these
|
|
numbers to 60, 30, and 24.
|
|
</para></formalpara>
|
|
|
|
<para>
|
|
Strictly speaking, all those numbers are approximations. Black and
|
|
white NTSC video was exactly 60 fields per second, but 60000/1001
|
|
was later chosen to accomodate color data while remaining compatible
|
|
with contemporary black and white televisions. Digital NTSC video
|
|
(such as on a DVD) is also 60000/1001 fields per second. From this,
|
|
interlaced and telecined video are derived to be 30000/1001 frames
|
|
per second; progressive video is 24000/1001 frames per second.
|
|
</para>
|
|
|
|
<para>
|
|
Older versions of the <application>MEncoder</application> documentation
|
|
and many archived mailing list posts refer to 59.94, 29.97, and 23.976.
|
|
All <application>MEncoder</application> documentation has been updated
|
|
to use the fractional values, and you should use them too.
|
|
</para>
|
|
|
|
<para>
|
|
<option>-ofps 23.976</option> is incorrect.
|
|
<option>-ofps 24000/1001</option> should be used instead.
|
|
</para>
|
|
|
|
<formalpara>
|
|
<title>How telecine is used.</title>
|
|
<para>
|
|
All video intended to be displayed on an NTSC
|
|
television set must be 60000/1001 fields per second. Made-for-TV movies
|
|
4 and shows are often filmed directly at 60000/1001 fields per second, but
|
|
the majority of cinema is filmed at 24 or 24000/1001 frames per
|
|
second. When cinematic movie DVDs are mastered, the video is then
|
|
converted for television using a process called telecine.
|
|
</para></formalpara>
|
|
|
|
<para>
|
|
On a DVD, the video is never actually stored as 60000/1001 fields per
|
|
second. For video that was originally 60000/1001, each pair of fields is
|
|
combined to form a frame, resulting in 30000/1001 frames per
|
|
second. Hardware DVD players then read a flag embedded in the video
|
|
stream to determine whether the odd- or even-numbered lines should
|
|
form the first field.
|
|
</para>
|
|
|
|
<para>
|
|
Usually, 24000/1001 frames per second content stays as it is when
|
|
encoded for a DVD, and the DVD player must perform telecining
|
|
on-the-fly. Sometimes, however, the video is telecined
|
|
<emphasis>before</emphasis> being stored on the DVD; even though it
|
|
was originally 24000/1001 frames per second, it becomes 60000/1001 fields per
|
|
second. When it is stored on the DVD, pairs of fields are combined to form
|
|
30000/1001 frames per second.
|
|
</para>
|
|
|
|
<para>
|
|
When looking at individual frames formed from 60000/1001 fields per
|
|
second video, telecined or otherwise, interlacing is clearly visible
|
|
wherever there is any motion, because one field (say, the
|
|
even-numbered lines) represents a moment in time 1/(60000/1001)
|
|
seconds later than the other. Playing interlaced video on a computer
|
|
looks ugly both because the monitor is higher resolution and because
|
|
the video is shown frame-after-frame instead of field-after-field.
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<title>Notes:</title>
|
|
<listitem><para>
|
|
This section only applies to NTSC DVDs, and not PAL.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
The example <application>MEncoder</application> lines throughout the
|
|
document are <emphasis role="bold">not</emphasis> intended for
|
|
actual use. They are simply the bare minimum required to encode the
|
|
pertaining video category. How to make good DVD rips or fine-tune
|
|
<systemitem class="library">libavcodec</systemitem> for maximal
|
|
quality is not within the scope of this document.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
There are a couple footnotes specific to this guide, linked like this:
|
|
<link linkend="menc-feat-telecine-footnotes">[1]</link>
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-telecine-ident">
|
|
<title>How to tell what type of video you have</title>
|
|
|
|
<sect3 id="menc-feat-telecine-ident-progressive">
|
|
<title>Progressive</title>
|
|
<para>
|
|
Progressive video was originally filmed at 24000/1001 fps, and stored
|
|
on the DVD without alteration.
|
|
</para>
|
|
|
|
<para>
|
|
When you play a progressive DVD in <application>MPlayer</application>,
|
|
<application>MPlayer</application> will print the following line as
|
|
soon as the movie begins to play:
|
|
|
|
<screen> demux_mpg: 24000/1001 fps progressive NTSC content detected, switching framerate.</screen>
|
|
|
|
From this point forward, demux_mpg should never say it finds
|
|
"30000/1001 fps NTSC content."
|
|
</para>
|
|
|
|
<para>
|
|
When you watch progressive video, you should never see any
|
|
interlacing. Beware, however, because sometimes there is a tiny bit
|
|
of telecine mixed in where you would not expect. I have encountered TV
|
|
show DVDs that have one second of telecine at every scene change, or
|
|
at seemingly random places. I once watched a DVD that had a
|
|
progressive first half, and the second half was telecined. If you
|
|
want to be <emphasis>really</emphasis> thorough, you can scan the
|
|
entire movie:
|
|
|
|
<screen>mplayer dvd://1 -nosound -vo null -benchmark</screen>
|
|
|
|
Using <option>-benchmark</option> makes
|
|
<application>MPlayer</application> play the movie as quickly as it
|
|
possibly can; still, depending on your hardware, it can take a
|
|
while. Every time demux_mpg reports a framerate change, the line
|
|
immediately above will show you the time at which the change
|
|
occurred.
|
|
</para>
|
|
|
|
<para>
|
|
Sometimes progressive video on DVDs is referred to as
|
|
"soft-telecine" because it is intended to
|
|
be telecined by the DVD player.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-ident-telecined">
|
|
<title>Telecined</title>
|
|
<para>
|
|
Telecined video was originally filmed at 24000/1001, but was telecined
|
|
<emphasis>before</emphasis> it was written to the DVD.
|
|
</para>
|
|
|
|
<para>
|
|
<application>MPlayer</application> does not (ever) report any
|
|
framerate changes when it plays telecined video.
|
|
</para>
|
|
|
|
<para>
|
|
Watching a telecined video, you will see interlacing artifacts that
|
|
seem to "blink": they repeatedly appear and disappear.
|
|
You can look closely at this by
|
|
<orderedlist>
|
|
<listitem>
|
|
<screen>mplayer dvd://1</screen>
|
|
</listitem>
|
|
<listitem><para>
|
|
Seek to a part with motion.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Use the <keycap>.</keycap> key to step forward one frame at a time.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Look at the pattern of interlaced-looking and progressive-looking
|
|
frames. If the pattern you see is PPPII,PPPII,PPPII,... then the
|
|
video is telecined. If you see some other pattern, then the video
|
|
may have been telecined using some non-standard method;
|
|
<application>MEncoder</application> cannot losslessly convert
|
|
non-standard telecine to progressive. If you do not see any
|
|
pattern at all, then it is most likely interlaced.
|
|
</para></listitem>
|
|
</orderedlist>
|
|
</para>
|
|
|
|
<para>
|
|
Sometimes telecined video on DVDs is referred to as
|
|
"hard-telecine". Since hard-telecine is already 60000/1001 fields
|
|
per second, the DVD player plays the video without any manipulation.
|
|
</para>
|
|
|
|
<para>
|
|
Another way to tell if your source is telecined or not is to play
|
|
the source with the <option>-vf pullup</option> and <option>-v</option>
|
|
command line options to see how <option>pullup</option> matches frames.
|
|
If the source is telecined, you should see on the console a 3:2 pattern
|
|
with <systemitem>0+.1.+2</systemitem> and <systemitem>0++1</systemitem>
|
|
alternating.
|
|
This technique has the advantage that you do not need to watch the
|
|
source to identify it, which could be useful if you wish to automate
|
|
the encoding procedure, or to carry out said procedure remotely via
|
|
a slow connection.
|
|
</para>
|
|
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-ident-interlaced">
|
|
<title>Interlaced</title>
|
|
<para>
|
|
Interlaced video was originally filmed at 60000/1001 fields per second,
|
|
and stored on the DVD as 30000/1001 frames per second. The interlacing effect
|
|
(often called "combing") is a result of combining pairs of
|
|
fields into frames. Each field is supposed to be 1/(60000/1001) seconds apart,
|
|
and when they are displayed simultaneously the difference is apparent.
|
|
</para>
|
|
|
|
<para>
|
|
As with telecined video, <application>MPlayer</application> should
|
|
not ever report any framerate changes when playing interlaced content.
|
|
</para>
|
|
|
|
<para>
|
|
When you view an interlaced video closely by frame-stepping with the
|
|
<keycap>.</keycap> key, you will see that every single frame is interlaced.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-ident-mixedpt">
|
|
<title>Mixed progressive and telecine</title>
|
|
<para>
|
|
All of a "mixed progressive and telecine" video was originally
|
|
24000/1001 frames per second, but some parts of it ended up being telecined.
|
|
</para>
|
|
|
|
<para>
|
|
When <application>MPlayer</application> plays this category, it will
|
|
(often repeatedly) switch back and forth between "30000/1001 fps NTSC"
|
|
and "24000/1001 fps progressive NTSC". Watch the bottom of
|
|
<application>MPlayer</application>'s output to see these messages.
|
|
</para>
|
|
|
|
<para>
|
|
You should check the "30000/1001 fps NTSC" sections to make sure
|
|
they are actually telecine, and not just interlaced.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-ident-mixedpi">
|
|
<title>Mixed progressive and interlaced</title>
|
|
<para>
|
|
In "mixed progressive and interlaced" content, progressive
|
|
and interlaced video have been spliced together.
|
|
</para>
|
|
|
|
<para>
|
|
This category looks just like "mixed progressive and telecine",
|
|
until you examine the 30000/1001 fps sections and see that they do not have the
|
|
telecine pattern.
|
|
</para>
|
|
</sect3>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-telecine-encode">
|
|
<title>How to encode each category</title>
|
|
<para>
|
|
As I mentioned in the beginning, example <application>MEncoder</application>
|
|
lines below are <emphasis role="bold">not</emphasis> meant to actually be used;
|
|
they only demonstrate the minimum parameters to properly encode each category.
|
|
</para>
|
|
|
|
<sect3 id="menc-feat-telecine-encode-progressive">
|
|
<title>Progressive</title>
|
|
<para>
|
|
Progressive video requires no special filtering to encode. The only
|
|
parameter you need to be sure to use is
|
|
<option>-ofps 24000/1001</option>. Otherwise, <application>MEncoder</application>
|
|
will try to encode at 30000/1001 fps and will duplicate frames.
|
|
</para>
|
|
|
|
<para>
|
|
<screen>mencoder dvd://1 -oac copy -ovc lavc -ofps 24000/1001</screen>
|
|
</para>
|
|
|
|
<para>
|
|
It is often the case, however, that a video that looks progressive
|
|
actually has very short parts of telecine mixed in. Unless you are
|
|
sure, it is safest to treat the video as
|
|
<link linkend="menc-feat-telecine-encode-mixedpt">mixed progressive and telecine</link>.
|
|
The performance loss is small
|
|
<link linkend="menc-feat-telecine-footnotes">[3]</link>.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-encode-telecined">
|
|
<title>Telecined</title>
|
|
<para>
|
|
Telecine can be reversed to retrieve the original 24000/1001 content,
|
|
using a process called inverse-telecine.
|
|
<application>MPlayer</application> contains several filters to
|
|
accomplish this; the best filter, <option>pullup</option>, is described
|
|
in the <link linkend="menc-feat-telecine-encode-mixedpt">mixed
|
|
progressive and telecine</link> section.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-encode-interlaced">
|
|
<title>Interlaced</title>
|
|
<para>
|
|
For most practical cases it is not possible to retrieve a complete
|
|
progressive video from interlaced content. The only way to do so
|
|
without losing half of the vertical resolution is to double the
|
|
framerate and try to "guess" what ought to make up the
|
|
corresponding lines for each field (this has drawbacks - see method
|
|
3).
|
|
</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>
|
|
|
|
Encode the video in interlaced form. Normally, interlacing wreaks
|
|
havoc with the encoder's ability to compress well, but
|
|
<systemitem class="library">libavcodec</systemitem> has two
|
|
parameters specifically for dealing with storing interlaced video a
|
|
bit better: <option> ildct</option> and <option>ilme</option>. Also,
|
|
using <option>mbd=2</option> is strongly recommended
|
|
<link linkend="menc-feat-telecine-footnotes">[2] </link> because it
|
|
will encode macroblocks as non-interlaced in places where there is
|
|
no motion. Note that <option>-ofps</option> is NOT needed here.
|
|
|
|
<screen>mencoder dvd://1 -oac copy -ovc lavc -lavcopts ildct:ilme:mbd=2</screen>
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Use a deinterlacing filter before encoding. There are several of
|
|
these filters available to choose from, each with its own advantages
|
|
and disadvantages. Consult <option>mplayer -pphelp</option> to see
|
|
what is available (grep for "deint"), and search the
|
|
<ulink url="http://www.mplayerhq.hu/homepage/design6/info.html#mailing_lists">
|
|
MPlayer mailing lists</ulink> to find many discussions about the
|
|
various filters. Again, the framerate is not changing, so no
|
|
<option>-ofps</option>. Also, deinterlacing should be done after
|
|
cropping <link linkend="menc-feat-telecine-footnotes">[1]</link> and
|
|
before scaling.
|
|
|
|
<screen>mencoder dvd://1 -oac copy -vf pp=lb -ovc lavc</screen>
|
|
</para></listitem>
|
|
<listitem><para>
|
|
Unfortunately, this option is buggy with
|
|
<application>MEncoder</application>; it ought to work well with
|
|
<application>MEncoder G2</application>, but that is not here yet. You
|
|
might experience crahes. Anyway, the purpose of <option> -vf
|
|
tfields</option> is to create a full frame out of each field, which
|
|
makes the framerate 60000/1001. The advantage of this approach is that no
|
|
data is ever lost; however, since each frame comes from only one
|
|
field, the missing lines have to be interpolated somehow. There are
|
|
no very good methods of generating the missing data, and so the
|
|
result will look a bit similar to when using some deinterlacing
|
|
filters. Generating the missing lines creates other issues, as well,
|
|
simply because the amount of data doubles. So, higher encoding
|
|
bitrates are required to maintain quality, and more CPU power is
|
|
used for both encoding and decoding. tfields has several different
|
|
options for how to create the missing lines of each frame. If you
|
|
use this method, then Reference the manual, and chose whichever
|
|
option looks best for your material. Note that when using
|
|
<option>tfields</option> you
|
|
<emphasis role="bold">have to</emphasis> specify both
|
|
<option>-fps</option> and <option>-ofps</option> to be twice the
|
|
framerate of your original source.
|
|
|
|
<screen>mencoder dvd://1 -oac copy -vf tfields=2 -ovc lavc -fps 60000/1001 -ofps 60000/1001</screen>
|
|
</para></listitem>
|
|
<listitem><para>
|
|
If you plan on downscaling dramatically, you can extract and encode
|
|
only one of the two fields. Of course, you will lose half the vertical
|
|
resolution, but if you plan on downscaling to at most 1/2 of the
|
|
original, the loss will not matter much. The result will be a
|
|
progressive 30000/1001 frames per second file. The procedure is to use
|
|
<option>-vf field</option>, then crop
|
|
<link linkend="menc-feat-telecine-footnotes">[1]</link> and scale
|
|
appropriately. Remember that you will have to adjust the scale to
|
|
compensate for the vertical resolution being halved.
|
|
<screen>mencoder dvd://1 -oac copy -vf field=0 -ovc lavc</screen>
|
|
</para></listitem>
|
|
</orderedlist>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-encode-mixedpt">
|
|
<title>Mixed progressive and telecine</title>
|
|
<para>
|
|
In order to turn mixed progressive and telecine video into entirely
|
|
progressive video, the telecined parts have to be
|
|
inverse-telecined. There are three ways to accomplish this,
|
|
described below. Note that you should
|
|
<emphasis role="bold">always</emphasis> inverse-telecine before any
|
|
rescaling; unless you really know what you are doing,
|
|
inverse-telecine before cropping, too
|
|
<link linkend="menc-feat-telecine-footnotes">[1]</link>.
|
|
<option>-ofps 24000/1001</option> is needed here because the output video
|
|
will be 24000/1001 frames per second.
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
<option>-vf pullup</option> is designed to inverse-telecine
|
|
telecined material while leaving progressive data alone. In order to
|
|
work properly, <option>pullup</option> <emphasis role="bold">must</emphasis>
|
|
be followed by the <option>softskip</option> filter or
|
|
else <application>MEncoder</application> will crash.
|
|
<option>pullup</option> is, however, the cleanest and most
|
|
accurate method available for encoding both telecine and
|
|
"mixed progressive and telecine".
|
|
|
|
<screen>mencoder dvd://1 -oac copy -vf pullup,softskip -ovc lavc -ofps 24000/1001</screen>
|
|
</para>
|
|
|
|
|
|
</listitem>
|
|
<listitem><para>
|
|
An older method
|
|
is to, rather than inverse-telecine the telecined parts, telecine
|
|
the non-telecined parts and then inverse-telecine the whole
|
|
video. Sound confusing? softpulldown is a filter that goes through
|
|
a video and makes the entire file telecined. If we follow
|
|
softpulldown with either <option>detc</option> or
|
|
<option>ivtc</option>, the final result will be entirely
|
|
progressive. <option>-ofps 24000/1001</option> is needed.
|
|
|
|
<screen>mencoder dvd://1 -oac copy -vf softpulldown,ivtc=1 -ovc lavc -ofps 24000/1001</screen>
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem><para>
|
|
I have not used <option>-vf filmdint</option> myself, but here is what
|
|
D Richard Felker III has to say:
|
|
|
|
<blockquote><para>It is OK, but IMO it tries to deinterlace rather
|
|
than doing inverse telecine too often (much like settop DVD
|
|
players & progressive TVs) which gives ugly flickering and
|
|
other artifacts. If you are going to use it, you at least need to
|
|
spend some time tuning the options and watching the output first
|
|
to make sure it is not messing up.</para></blockquote>
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-telecine-encode-mixedpi">
|
|
<title>Mixed progressive and interlaced</title>
|
|
<para>
|
|
There are two options for dealing with this category, each of
|
|
which is a compromise. You should decide based on the
|
|
duration/location of each type.
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
Treat it as progressive. The interlaced parts will look interlaced,
|
|
and some of the interlaced fields will have to be dropped, resulting
|
|
in a bit of uneven jumpiness. You can use a postprocessing filter if
|
|
you want to, but it may slightly degrade the progressive parts.
|
|
</para>
|
|
|
|
<para>
|
|
This option should definitely not be used if you want to eventually
|
|
display the video on an interlaced device (with a TV card, for
|
|
example). If you have interlaced frames in a 24000/1001 frames per
|
|
second video, they will be telecined along with the progressive
|
|
frames. Half of the interlaced "frames" will be displayed for three
|
|
fields' duration (3/(60000/1001) seconds), resulting in a flicking
|
|
"jump back in time" effect that looks quite bad. If you
|
|
even attempt this, you <emphasis role="bold">must</emphasis> use a
|
|
deinterlacing filter like <option>lb</option> or
|
|
<option>l5</option>.
|
|
</para>
|
|
|
|
<para>
|
|
It may also be a bad idea for progressive display, too. It will drop
|
|
pairs of consecutive interlaced fields, resulting in a discontinuity
|
|
that can be more visible than with the second method, which shows
|
|
some progressive frames twice. 30000/1001 frames per second interlaced
|
|
video is already a bit choppy because it really should be shown at
|
|
60000/1001 fields per second, so the duplicate frames do not stand out as
|
|
much.
|
|
</para>
|
|
|
|
<para>
|
|
Either way, it is best to consider your content and how you intend to
|
|
display it. If your video is 90% progressive and you never intend to
|
|
show it on a TV, you should favor a progressive approach. If it is
|
|
only half progressive, you probably want to encode it as if it is all
|
|
interlaced.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem><para>
|
|
Treat it as interlaced. Some frames of the progressive parts will
|
|
need to be duplicated, resulting in uneven jumpiness. Again,
|
|
deinterlacing filters may slightly degrade the progressive parts.
|
|
</para></listitem>
|
|
|
|
</itemizedlist>
|
|
</sect3>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-telecine-footnotes">
|
|
<title>Footnotes</title>
|
|
<orderedlist>
|
|
<listitem><formalpara>
|
|
<title>About cropping:</title>
|
|
<para>
|
|
Video data on DVDs are stored in a format called YUV 4:2:0. In YUV
|
|
video, luma ("brightness") and chroma ("color")
|
|
are stored separately. Because the human eye is somewhat less
|
|
sensitive to color than it is to brightness, in a YUV 4:2:0 picture
|
|
there is only one chroma pixel for every four luma pixels. In a
|
|
progressive picture, each square of four luma pixels (two on each
|
|
side) has one common chroma pixel. You must crop progressive YUV
|
|
4:2:0 to even resolutions, and use even offsets. For example,
|
|
<option>crop=716:380:2:26</option> is OK but
|
|
<option>crop=716:380:3:26 </option> is not.
|
|
</para>
|
|
</formalpara>
|
|
|
|
<para>
|
|
When you are dealing with interlaced YUV 4:2:0, the situation is a
|
|
bit more complicated. Instead of every four luma pixels in the
|
|
<emphasis>frame</emphasis> sharing a chroma pixel, every four luma
|
|
pixels in each <emphasis> field</emphasis> share a chroma
|
|
pixel. When fields are interlaced to form a frame, each scanline is
|
|
one pixel high. Now, instead of all four luma pixels being in a
|
|
square, there are two pixels side-by-side, and the other two pixels
|
|
are side-by-side two scanlines down. The two luma pixels in the
|
|
intermediate scanline are from the other field, and so share a
|
|
different chroma pixel with two luma pixels two scanlines away. All
|
|
this confusion makes it necessary to have vertical crop dimensions
|
|
and offsets be multiples of four. Horizontal can stay even.
|
|
</para>
|
|
|
|
<para>
|
|
For telecined video, I recommend that cropping take place after
|
|
inverse telecining. Once the video is progressive you only need to
|
|
crop by even numbers. If you really want to gain the slight speedup
|
|
that cropping first may offer, you must crop vertically by multiples
|
|
of four or else the inverse-telecine filter will not have proper data.
|
|
</para>
|
|
|
|
<para>
|
|
For interlaced (not telecined) video, you must always crop
|
|
vertically by multiples of four unless you use <option>-vf
|
|
field</option> before cropping.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem><formalpara>
|
|
<title>About encoding parameters and quality:</title>
|
|
<para>
|
|
Just because I recommend <option>mbd=2</option> here does not mean it
|
|
should not be used elsewhere. Along with <option>trell</option>,
|
|
<option>mbd=2</option> is one of the two
|
|
<systemitem class="library">libavcodec</systemitem> options that
|
|
increases quality the most, and you should always use at least those
|
|
two unless the drop in encoding speed is prohibitive (e.g. realtime
|
|
encoding). There are many other options to
|
|
<systemitem class="library">libavcodec</systemitem> that increase
|
|
encoding quality (and decrease encoding speed) but that is beyond
|
|
the scope of this document.
|
|
</para>
|
|
</formalpara>
|
|
</listitem>
|
|
|
|
<listitem><formalpara>
|
|
<title>About the performance of pullup:</title>
|
|
<para>
|
|
It is safe to use <option>pullup</option> (along with <option>softskip
|
|
</option>) on progressive video, and is usually a good idea unless
|
|
the source has been definitively verified to be entirely progressive.
|
|
The performace loss is small for most cases. On a bare-minimum encode,
|
|
<option>pullup</option> causes <application>MEncoder</application> to
|
|
be 50% slower. Adding sound processing and advanced <option>lavcopts
|
|
</option> overshadows that difference, bringing the performance
|
|
decrease of using <option>pullup</option> down to 2%.
|
|
</para>
|
|
</formalpara>
|
|
</listitem>
|
|
|
|
</orderedlist>
|
|
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
|
|
<sect1 id="menc-feat-enc-libavcodec">
|
|
<title>Encoding with the <systemitem class="library">libavcodec</systemitem>
|
|
codec family</title>
|
|
|
|
<para>
|
|
<link linkend="ffmpeg"><systemitem class="library">libavcodec</systemitem></link>
|
|
provides simple encoding to a lot of interesting video and audio formats.
|
|
You can encode to the following codecs (more or less up to date):
|
|
</para>
|
|
|
|
<sect2 id="menc-feat-enc-libavcodec-video-codecs">
|
|
<title><systemitem class="library">libavcodec</systemitem>'s video codecs</title>
|
|
|
|
<para>
|
|
<informaltable frame="all">
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row><entry>Video codec name</entry><entry>Description</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row><entry>mjpeg</entry><entry>
|
|
Motion JPEG
|
|
</entry></row>
|
|
<row><entry>ljpeg</entry><entry>
|
|
lossless JPEG
|
|
</entry></row>
|
|
<row><entry>h261</entry><entry>
|
|
H.261
|
|
</entry></row>
|
|
<row><entry>h263</entry><entry>
|
|
H.263
|
|
</entry></row>
|
|
<row><entry>h263p</entry><entry>
|
|
H.263+
|
|
</entry></row>
|
|
<row><entry>mpeg4</entry><entry>
|
|
ISO standard MPEG-4 (DivX 5, XviD compatible)
|
|
</entry></row>
|
|
<row><entry>msmpeg4</entry><entry>
|
|
pre-standard MPEG-4 variant by MS, v3 (AKA DivX3)
|
|
</entry></row>
|
|
<row><entry>msmpeg4v2</entry><entry>
|
|
pre-standard MPEG-4 by MS, v2 (used in old ASF files)
|
|
</entry></row>
|
|
<row><entry>wmv1</entry><entry>
|
|
Windows Media Video, version 1 (AKA WMV7)
|
|
</entry></row>
|
|
<row><entry>wmv2</entry><entry>
|
|
Windows Media Video, version 2 (AKA WMV8)
|
|
</entry></row>
|
|
<row><entry>rv10</entry><entry>
|
|
RealVideo 1.0
|
|
</entry></row>
|
|
<row><entry>rv20</entry><entry>
|
|
RealVideo 2.0
|
|
</entry></row>
|
|
<row><entry>mpeg1video</entry><entry>
|
|
MPEG-1 video
|
|
</entry></row>
|
|
<row><entry>mpeg2video</entry><entry>
|
|
MPEG-2 video
|
|
</entry></row>
|
|
<row><entry>huffyuv</entry><entry>
|
|
lossless compression
|
|
</entry></row>
|
|
<row><entry>asv1</entry><entry>
|
|
ASUS Video v1
|
|
</entry></row>
|
|
<row><entry>asv2</entry><entry>
|
|
ASUS Video v2
|
|
</entry></row>
|
|
<row><entry>ffv1</entry><entry>
|
|
FFmpeg's lossless video codec
|
|
</entry></row>
|
|
<row><entry>svq1</entry><entry>
|
|
Sorenson video 1
|
|
</entry></row>
|
|
<row><entry>flv</entry><entry>
|
|
Sorenson H.263 used in Flash Video
|
|
</entry></row>
|
|
<row><entry>dvvideo</entry><entry>
|
|
Sony Digital Video
|
|
</entry></row>
|
|
<row><entry>snow</entry><entry>
|
|
FFmpeg's experimental wavelet-based codec
|
|
</entry></row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
|
|
The first column contains the codec names that should be passed after the
|
|
<literal>vcodec</literal> config, like: <option>-lavcopts vcodec=msmpeg4</option>
|
|
</para>
|
|
<informalexample>
|
|
<para>
|
|
An example with MJPEG compression:
|
|
<screen>mencoder dvd://2 -o title2.avi -ovc lavc -lavcopts vcodec=mjpeg -oac copy</screen>
|
|
</para>
|
|
</informalexample>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-enc-libavcodec-audio-codecs">
|
|
<title><systemitem class="library">libavcodec</systemitem>'s audio codecs</title>
|
|
<para>
|
|
<informaltable frame="all">
|
|
<tgroup cols="2">
|
|
<thead>
|
|
<row><entry>Audio codec name</entry><entry>Description</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>mp2</entry>
|
|
<entry>MPEG Layer 2</entry>
|
|
</row>
|
|
<row>
|
|
<entry>ac3</entry>
|
|
<entry>AC3, AKA Dolby Digital</entry>
|
|
</row>
|
|
<row>
|
|
<entry>adpcm_ima_wav</entry>
|
|
<entry>IMA adaptive PCM (4 bits per sample, 4:1 compression)</entry>
|
|
</row>
|
|
<row>
|
|
<entry>sonic</entry>
|
|
<entry>experimental lossy/lossless codec</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
|
|
The first column contains the codec names that should be passed after the
|
|
<literal>acodec</literal> option, like: <option>-lavcopts acodec=ac3</option>
|
|
</para>
|
|
|
|
<informalexample>
|
|
<para>
|
|
An example with AC3 compression:
|
|
<screen>mencoder dvd://2 -o title2.avi -oac lavc -lavcopts acodec=ac3 -ovc copy</screen>
|
|
</para>
|
|
</informalexample>
|
|
|
|
<para>
|
|
Contrary to <systemitem class="library">libavcodec</systemitem>'s video
|
|
codecs, its audio codecs do not make a wise usage of the bits they are
|
|
given as they lack some minimal psychoacoustic model (if at all)
|
|
which most other codec implementations feature.
|
|
However, note that all these audio codecs are very fast and work
|
|
out-of-the-box everywhere <application>MEncoder</application> has been
|
|
compiled with <systemitem class="library">libavcodec</systemitem> (which
|
|
is the case most of time), and do not depend on external libraries.
|
|
</para>
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-lavc-encoding-options">
|
|
<title>Encoding options of libavcodec</title>
|
|
|
|
<para>
|
|
Ideally, you would probably want to be able to just tell the encoder to switch
|
|
into "high quality" mode and move on.
|
|
That would probably be nice, but unfortunately hard to implement as different
|
|
encoding options yield different quality results depending on the source material.
|
|
That is because compression depends on the visual properties of the video
|
|
in question.
|
|
For example, anime and live action have very different properties and
|
|
thus require different options to obtain optimum encoding.
|
|
The good news is that some options should never be left out, like
|
|
<option>mbd=2</option>, <option>trell</option>, and <option>v4mv</option>.
|
|
See below for a detailed description of common encoding options.
|
|
</para>
|
|
|
|
|
|
<itemizedlist>
|
|
<title>Options to adjust:</title>
|
|
<listitem><para>
|
|
<emphasis role="bold">vmax_b_frames</emphasis>: 1 or 2 is good, depending on
|
|
the movie.
|
|
Note that if you need to have your encode be decodable by DivX5, you
|
|
need to activate closed GOP support, using
|
|
<systemitem class="library">libavcodec</systemitem>'s <option>cgop</option>
|
|
option, but you need to deactivate scene detection, which
|
|
is not a good idea as it will hurt encode efficiency a bit.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vb_strategy=1</emphasis>: helps in high-motion scenes.
|
|
On some videos, vmax_b_frames may hurt quality, but vmax_b_frames=2 along
|
|
with vb_strategy=1 helps.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">dia</emphasis>: motion search range. Bigger is better
|
|
and slower.
|
|
Negative values are a completely different scale.
|
|
Good values are -1 for a fast encode, or 2-4 for slower.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">predia</emphasis>: motion search pre-pass.
|
|
Not as important as dia. Good values are 1 (default) to 4. Requires preme=2
|
|
to really be useful.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">cmp, subcmp, precmp</emphasis>: Comparison function for
|
|
motion estimation.
|
|
Experiment with values of 0 (default), 2 (hadamard), 3 (dct), and 6 (rate
|
|
distortion).
|
|
0 is fastest, and sufficient for precmp.
|
|
For cmp and subcmp, 2 is good for anime, and 3 is good for live action.
|
|
6 may or may not be slightly better, but is slow.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">last_pred</emphasis>: Number of motion predictors to
|
|
take from the previous frame.
|
|
1-3 or so help at little speed cost.
|
|
Higher values are slow for no extra gain.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">cbp, mv0</emphasis>: Controls the selection of macroblocks.
|
|
Small speed cost for small quality gain.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">qprd</emphasis>: adaptive quantization based on the
|
|
macroblock's complexity.
|
|
May help or hurt depending on the video and other options.
|
|
This can cause artifacts unless you set vqmax to some reasonably small value
|
|
(6 is good, maybe as low as 4); vqmin=1 should also help.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">qns</emphasis>: very slow, especially when combined
|
|
with qprd.
|
|
This option will make the encoder minimize noise due to compression
|
|
artifacts instead of making the encoded video strictly match the source.
|
|
Do not use this unless you have already tweaked everything else as far as it
|
|
will go and the results still are not good enough.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vqcomp</emphasis>: Tweak ratecontrol.
|
|
What values are good depends on the movie.
|
|
You can safely leave this alone if you want.
|
|
Reducing vqcomp puts more bits on low-complexity scenes, increasing it puts
|
|
them on high-complexity scenes (default: 0.5, range: 0-1. recommended range:
|
|
0.5-0.7).
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vlelim, vcelim</emphasis>: Sets the single coefficient
|
|
elimination threshold for luminance and chroma planes.
|
|
These are encoded separately in all MPEG-like algorithms.
|
|
The idea behind these options is to use some good heuristics to determine
|
|
when the change in a block is less than the threshold you specify, and in
|
|
such a case, to just encode the block as "no change".
|
|
This saves bits and perhaps speeds up encoding. vlelim=-4 and vcelim=9
|
|
seem to be good for live movies, but seem not to help with anime;
|
|
when encoding animation, you should probably leave them unchanged.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">qpel</emphasis>: Quarter pixel motion estimation.
|
|
MPEG-4 uses half pixel precision for its motion search by default,
|
|
therefore this option comes with an overhead as more information will be
|
|
stored in the encoded file.
|
|
The compression gain/loss depends on the movie, but it is usually not very
|
|
effective on anime.
|
|
qpel always incurs a significant cost in CPU decode time (+25% in
|
|
practice).
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">psnr</emphasis>: does not affect the actual encoding,
|
|
but writes a log file giving the type/size/quality of each frame, and
|
|
prints a summary of PSNR (Peak Signal to Noise Ratio) at the end.
|
|
</para></listitem>
|
|
|
|
</itemizedlist>
|
|
|
|
<itemizedlist>
|
|
<title>Options not recommended to play with:</title>
|
|
<listitem><para>
|
|
<emphasis role="bold">vme</emphasis>: The default is best.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">lumi_mask, dark_mask</emphasis>: Psychovisual adaptive
|
|
quantization.
|
|
You do not want to play with those options if you care about quality.
|
|
Reasonable values may be effective in your case, but be warned this is very
|
|
subjective.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">scplx_mask</emphasis>: Tries to prevent blocky
|
|
artifacts, but postprocessing is better.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-mpeg4-lavc-example-settings">
|
|
<title>Encoding setting examples</title>
|
|
|
|
<para>
|
|
The following settings are examples of different encoding
|
|
option combinations that affect the speed vs quality tradeoff
|
|
at the same target bitrate.
|
|
</para>
|
|
|
|
<para>
|
|
All the encoding settings were tested on a 720x448 @30000/1001 fps
|
|
video sample, the target bitrate was 900kbps, and the machine was an
|
|
AMD-64 3400+ at 2400 Mhz in 64 bits mode.
|
|
Each encoding setting features the measured encoding speed (in
|
|
frames per second) and the PSNR loss (in dB) compared to the "very
|
|
high quality" setting.
|
|
Please understand that depending on your source, your machine type
|
|
and development advancements, you may get very different results.
|
|
</para>
|
|
|
|
<para>
|
|
<informaltable frame="all">
|
|
<tgroup cols="4">
|
|
<thead>
|
|
<row><entry>Description</entry><entry>Encoding options</entry><entry>speed (in fps)</entry><entry>Relative PSNR loss (in dB)</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>Very high quality</entry>
|
|
<entry><option>vcodec=mpeg4:mbd=2:mv0:trell:v4mv:cbp:last_pred=3:predia=2:dia=2:vmax_b_frames=2:vb_strategy=1:precmp=2:cmp=2:subcmp=2:preme=2:vme=5:naq:qns=2</option></entry>
|
|
<entry>6fps</entry>
|
|
<entry>0dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>High quality</entry>
|
|
<entry><option>vcodec=mpeg4:mbd=2:trell:v4mv:last_pred=2:dia=-1:vmax_b_frames=2:vb_strategy=1:cmp=3:subcmp=3:precmp=0:vqcomp=0.6:turbo</option></entry>
|
|
<entry>15fps</entry>
|
|
<entry>-0.5dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Fast</entry>
|
|
<entry><option>vcodec=mpeg4:mbd=2:trell:v4mv:turbo</option></entry>
|
|
<entry>42fps</entry>
|
|
<entry>-0.74dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Realtime</entry>
|
|
<entry><option>vcodec=mpeg4:mbd=2:turbo</option></entry>
|
|
<entry>54fps</entry>
|
|
<entry>-1.21dB</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="custommatrices"><title>Custom inter/intra matrices</title>
|
|
|
|
<para>
|
|
With this feature of
|
|
<link linkend="ffmpeg"><systemitem class="library">libavcodec</systemitem></link>
|
|
you are able to set custom inter (I-frames/keyframes) and intra
|
|
(P-frames/predicted frames) matrices. It is supported by many of the codecs:
|
|
<systemitem>mpeg1video</systemitem> and <systemitem>mpeg2video</systemitem>
|
|
are reported as working.
|
|
</para>
|
|
|
|
<para>
|
|
A typical usage of this feature is to set the matrices preferred by the
|
|
<ulink url="http://www.kvcd.net/">KVCD</ulink> specifications.
|
|
</para>
|
|
|
|
<para>
|
|
The <emphasis role="bold">KVCD "Notch" Quantization Matrix:</emphasis>
|
|
</para>
|
|
|
|
<para>
|
|
Intra:
|
|
<screen>
|
|
8 9 12 22 26 27 29 34
|
|
9 10 14 26 27 29 34 37
|
|
12 14 18 27 29 34 37 38
|
|
22 26 27 31 36 37 38 40
|
|
26 27 29 36 39 38 40 48
|
|
27 29 34 37 38 40 48 58
|
|
29 34 37 38 40 48 58 69
|
|
34 37 38 40 48 58 69 79
|
|
</screen>
|
|
|
|
Inter:
|
|
<screen>
|
|
16 18 20 22 24 26 28 30
|
|
18 20 22 24 26 28 30 32
|
|
20 22 24 26 28 30 32 34
|
|
22 24 26 30 32 32 34 36
|
|
24 26 28 32 34 34 36 38
|
|
26 28 30 32 34 36 38 40
|
|
28 30 32 34 36 38 42 42
|
|
30 32 34 36 38 40 42 44
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
Usage:
|
|
<screen>
|
|
$ mencoder <replaceable>input.avi</replaceable> -o <replaceable>output.avi</replaceable> -oac copy -ovc lavc -lavcopts inter_matrix=...:intra_matrix=...
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
<screen>
|
|
$ mencoder <replaceable>input.avi</replaceable> -ovc lavc -lavcopts
|
|
vcodec=mpeg2video:intra_matrix=8,9,12,22,26,27,29,34,9,10,14,26,27,29,34,37,
|
|
12,14,18,27,29,34,37,38,22,26,27,31,36,37,38,40,26,27,29,36,39,38,40,48,27,
|
|
29,34,37,38,40,48,58,29,34,37,38,40,48,58,69,34,37,38,40,48,58,69,79
|
|
:inter_matrix=16,18,20,22,24,26,28,30,18,20,22,24,26,28,30,32,20,22,24,26,
|
|
28,30,32,34,22,24,26,30,32,32,34,36,24,26,28,32,34,34,36,38,26,28,30,32,34,
|
|
36,38,40,28,30,32,34,36,38,42,42,30,32,34,36,38,40,42,44 -oac copy -o svcd.mpg
|
|
</screen>
|
|
</para>
|
|
</sect2>
|
|
|
|
|
|
<sect2 id="menc-feat-dvd-mpeg4-example">
|
|
<title>Example</title>
|
|
|
|
<para>
|
|
So, you have just bought your shiny new copy of Harry Potter and the Chamber
|
|
of Secrets (widescreen edition, of course), and you want to rip this DVD
|
|
so that you can add it to your Home Theatre PC. This is a region 1 DVD,
|
|
so it is NTSC. The example below will still apply to PAL, except you will
|
|
omit <option>-ofps 24000/1001</option> (because the output framerate is the
|
|
same as the input framerate), and of course the crop dimensions will be
|
|
different.
|
|
</para>
|
|
|
|
<para>
|
|
After running <option>mplayer dvd://1</option>, we follow the process
|
|
detailed in the section <link linkend="menc-feat-telecine">How to deal
|
|
with telecine and interlacing in NTSC DVDs</link> and discover that it is
|
|
24000/1001 fps progressive video, which means that we need not use an inverse
|
|
telecine filter, such as <option>pullup</option> or
|
|
<option>filmdint</option>.
|
|
</para>
|
|
|
|
<para>
|
|
Next, we want to determine the appropriate crop rectangle, so we use the
|
|
cropdetect filter:
|
|
|
|
<screen>mplayer dvd://1 -vf cropdetect</screen>
|
|
|
|
Make sure you seek to a fully filled frame (such as a bright scene), and
|
|
you will see in <application>MPlayer</application>'s console output:
|
|
|
|
<screen>crop area: X: 0..719 Y: 57..419 (-vf crop=720:362:0:58)</screen>
|
|
|
|
We then play the movie back with this filter to test its correctness:
|
|
|
|
<screen>mplayer dvd://1 -vf crop=720:362:0:58</screen>
|
|
|
|
And we see that it looks perfectly fine. Next, we ensure the width and
|
|
height are a multiple of 16. The width is fine, however the height is
|
|
not. Since we did not fail 7th grade math, we know that the nearest
|
|
multiple of 16 lower than 362 is 352.
|
|
</para>
|
|
|
|
<para>
|
|
We could just use <option>crop=720:352:0:58</option>, but it would be nice
|
|
to take a little off the top and a little off the bottom so that we
|
|
retain the center. We have shrunk the height by 10 pixels, but we do not
|
|
want to increase the y-offset by 5-pixels since that is an odd number and
|
|
will adversely affect quality. Instead, we will increase the y-offset by
|
|
4 pixels:
|
|
|
|
<screen>mplayer dvd://1 -vf crop=720:352:0:62</screen>
|
|
|
|
Another reason to shave pixels from both the top and the bottom is that we
|
|
ensure we have eliminated any half-black pixels if they exist. Note that if
|
|
your video is telecined, make sure the <option>pullup</option> filter (or
|
|
whichever inverse telecine filter you decide to use) appears in the filter
|
|
chain before you crop. If it is interlaced, deinterlace before cropping.
|
|
(If you choose to preserve the interlaced video, then make sure your
|
|
vertical crop offset is a multiple of 4.)
|
|
</para>
|
|
|
|
<para>
|
|
If you are really concerned about losing those 10 pixels, you might
|
|
prefer instead to scale the dimensions down to the nearest multiple of 16.
|
|
The filter chain would look like:
|
|
|
|
<screen>-vf crop=720:362:0:58,scale=720:352</screen>
|
|
|
|
Scaling the video down like this will mean that some small amount of
|
|
detail is lost, though it probably will not be perceptible. Scaling up will
|
|
result in lower quality (unless you increase the bitrate). Cropping
|
|
discards those pixels altogether. It is a tradeoff that you will want to
|
|
consider for each circumstance. For example, if the DVD video was made
|
|
for television, you might want to avoid vertical scaling, since the line
|
|
sampling corresponds to the way the content was originally recorded.
|
|
</para>
|
|
|
|
<para>
|
|
On inspection, we see that our movie has a fair bit of action and high
|
|
amounts of detail, so we pick 2400Kbit for our bitrate.
|
|
</para>
|
|
|
|
<para>
|
|
We are now ready to do the two pass encode. Pass one:
|
|
|
|
<screen>mencoder dvd://1 -ofps 24000/1001 -oac copy -vf crop=720:352:0:62,hqdn3d=2:1:2 -ovc lavc \
|
|
-lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:mbcmp=3:autoaspect:vpass=1 \
|
|
-o Harry_Potter_2.avi</screen>
|
|
|
|
And pass two is the same, except that we specify <option>vpass=2</option>:
|
|
|
|
<screen>mencoder dvd://1 -ofps 24000/1001 -oac copy -vf crop=720:352:0:62,hqdn3d=2:1:2 -ovc lavc \
|
|
-lavcopts vcodec=mpeg4:vbitrate=2400:v4mv:mbd=2:trell:cmp=3:subcmp=3:mbcmp=3:autoaspect:vpass=2 \
|
|
-o Harry_Potter_2.avi</screen>
|
|
</para>
|
|
|
|
<para>
|
|
The options <option>v4mv:mbd=2:trell</option> will greatly increase the
|
|
quality at the expense of encoding time. There is little reason to leave
|
|
these options out when the primary goal is quality. The options
|
|
<option>cmp=3:subcmp=3:mbcmp=3</option> select a comparison function that
|
|
yields higher quality than the defaults. You might try experimenting with
|
|
this parameter (refer to the man page for the possible values) as
|
|
different functions can have a large impact on quality depending on the
|
|
source material. For example, if you find
|
|
<systemitem class="library">libavcodec</systemitem> produces too much
|
|
blocky artifacting, you could try selecting the experimental NSSE as
|
|
comparison function via <option>*cmp=10</option>.
|
|
</para>
|
|
|
|
<para>
|
|
For this movie, the resulting AVI will be 138 minutes long and nearly
|
|
3GB. And because you said that file size does not matter, this is a
|
|
perfectly acceptable size. However, if you had wanted it smaller, you
|
|
could try a lower bitrate. Increasing bitrates have diminishing
|
|
returns, so while we might clearly see an improvement from 1800Kbit to
|
|
2000Kbit, it might not be so noticeable above 2000Kbit. Feel
|
|
free to experiment until you are happy.
|
|
</para>
|
|
|
|
<para>
|
|
Because we passed the source video through a denoise filter, you may want
|
|
to add some of it back during playback. This, along with the
|
|
<option>spp</option> post-processing filter, drastically improves the
|
|
perception of quality and helps eliminate blocky artifacts in the video.
|
|
With <application>MPlayer</application>'s <option>autoq</option> option,
|
|
you can vary the amount of post-processing done by the spp filter
|
|
depending on available CPU. Also, at this point, you may want to apply
|
|
gamma and/or color correction to best suit your display. For example:
|
|
|
|
<screen>mplayer Harry_Potter_2.avi -vf spp,noise=9ah:5ah,eq2=1.2 -autoq 3</screen>
|
|
|
|
</para>
|
|
</sect2>
|
|
</sect1>
|
|
|
|
|
|
<sect1 id="menc-feat-xvid">
|
|
<title>Encoding with the <systemitem class="library">XviD</systemitem>
|
|
codec</title>
|
|
<para>
|
|
<systemitem class="library">XviD</systemitem> is a free library for
|
|
encoding MPEG-4 ASP video streams.
|
|
Before starting to encode, you need to <link linkend="xvid">
|
|
set up <application>MEncoder</application> to support it</link>.
|
|
</para>
|
|
<para>
|
|
This guide mainly aims at featuring the same kind of information
|
|
as x264's encoding guide.
|
|
Therefore, please begin by reading
|
|
<link linkend="menc-feat-x264-encoding-options-intro">the first part</link>
|
|
of that guide.
|
|
</para>
|
|
|
|
|
|
<sect2 id="menc-feat-xvid-intro">
|
|
<title>What options should I use to get the best results?</title>
|
|
|
|
<para>
|
|
Please begin by reviewing the
|
|
<systemitem class="library">XviD</systemitem> section of
|
|
<application>MPlayer</application>'s man page.
|
|
This section is intended to be a supplement to the man page.
|
|
</para>
|
|
<para>
|
|
The XviD default settings are already a good tradeoff between
|
|
speed and quality, therefore you can safely stick to them if
|
|
the following section puzzles you.
|
|
</para>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-xvid-encoding-options">
|
|
<title>Encoding options of <systemitem class="library">XviD</systemitem></title>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
<emphasis role="bold">vhq</emphasis>
|
|
This setting affects the macroblock decision algorithm, where the
|
|
higher the setting, the wiser the decision.
|
|
The default setting may be safely used for every encode, while
|
|
higher settings always help PSNR but are significantly slower.
|
|
Please note that a better PSNR does not necessarily mean
|
|
that the picture will look better, but tells you that it is
|
|
closer to the original.
|
|
Turning it off will noticeably speed up encoding; if speed is
|
|
critical for you, the tradeoff may be worth it.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">bvhq</emphasis>
|
|
This does the same job as vhq, but does it on B-frames.
|
|
It has a negligible impact on speed, and slightly improves quality
|
|
(around +0.1dB PSNR).
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">max_bframes</emphasis>
|
|
A higher number of consecutive allowed B-frames usually improves
|
|
compressibility, although it may also lead to more blocking artifacts.
|
|
The default setting is a good tradeoff between compressibility and
|
|
quality, but you may increase it up to 3 if you are bitrate-starved.
|
|
You may also decrease it to 1 or 0 if you are aiming at perfect
|
|
quality, though in that case you should make sure your
|
|
target bitrate is high enough to ensure that the encoder does not
|
|
have to increase quantizers to reach it.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">bf_threshold</emphasis>
|
|
This controls the B-frame sensitivity of the encoder, where a higher
|
|
value leads to more B-frames being used (and vice versa).
|
|
This setting is to be used together with <option>max_bframes</option>;
|
|
if you are bitrate-starved, you should increase both
|
|
<option>max_bframes</option> and <option>bf_threshold</option>,
|
|
while you may increase <option>max_bframes</option> and reduce
|
|
<option>bf_threshold</option> so that the encoder may use more
|
|
B-frames in places that only <emphasis role="bold">really</emphasis>
|
|
need them.
|
|
A low number of <option>max_bframes</option> and a high value of
|
|
<option>bf_threshold</option> is probably not a wise choice as it
|
|
will force the encoder to put B-frames in places that would not
|
|
benefit from them, therefore reducing visual quality.
|
|
However, if you need to be compatible with standalone players that
|
|
only support old DivX profiles (which only supports up to 1
|
|
consecutive B-frame), this would be your only way to
|
|
increase compressibility through using B-frames.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">trellis</emphasis>
|
|
Optimizes the quantization process to get an optimal tradeoff
|
|
between PSNR and bitrate, which allows significant bit saving.
|
|
These bits will in return be spent elsewhere on the video,
|
|
raising overall visual quality.
|
|
You should always leave it on as its impact on quality is huge.
|
|
Even if you are looking for speed, do not disable it until you
|
|
have turned down <option>vhq</option> and all other more
|
|
CPU-hungry options to the minimum.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">hq_ac</emphasis>
|
|
Activates a better coefficient cost estimation method, which slightly
|
|
reduces filesize by around 0.15 to 0.19% (which corresponds to less
|
|
than 0.01dB PSNR increase), while having a negligible impact on speed.
|
|
It is therefore recommended to always leave it on.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">cartoon</emphasis>
|
|
Designed to better encode cartoon content, and has no impact on
|
|
speed as it just tunes the mode decision heuristics for this type
|
|
of content.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">me_quality</emphasis>
|
|
This setting is to control the precision of the motion estimation.
|
|
The higher <option>me_quality</option>, the more
|
|
precise the estimation of the original motion will be, and the
|
|
better the resulting clip will capture the original motion.
|
|
</para>
|
|
<para>
|
|
The default setting is best in all cases;
|
|
thus it is not recommended to turn it down unless you are
|
|
really looking for speed, as all the bits saved by a good motion
|
|
estimation would be spent elsewhere, raising overall quality.
|
|
Therefore, do not go any lower than 5, and even that only as a last
|
|
resort.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">chroma_me</emphasis>
|
|
Improves motion estimation by also taking the chroma (color)
|
|
information into account, whereas <option>me_quality</option>
|
|
alone only uses luma (grayscale).
|
|
This slows down encoding by 5-10% but improves visual quality
|
|
quite a bit by reducing blocking effects and reduces filesize by
|
|
around 1.3%.
|
|
If you are looking for speed, you should disable this option before
|
|
starting to consider reducing <option>me_quality</option>.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">chroma_opt</emphasis>
|
|
Is intended to increase chroma image quality around pure
|
|
white/black edges, rather than improving compression.
|
|
This can help to reduce the "red stairs" effect.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">lumi_mask</emphasis>
|
|
Tries to give less bitrate to part of the picture that the
|
|
human eye cannot see very well, which should allow the encoder
|
|
to spend the saved bits on more important parts of the picture.
|
|
The quality of the encode yielded by this option highly depends
|
|
on personal preferences and on the type and monitor settings
|
|
used to watch it (typically, it will not look as good if it is
|
|
bright or if it is a TFT monitor).
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">qpel</emphasis>
|
|
Raise the number of candidate motion vectors by increasing
|
|
the precision of the motion estimation from halfpel to
|
|
quarterpel.
|
|
The idea is to find better motion vectors which will in return
|
|
reduce bitrate (hence increasing quality).
|
|
However, motion vectors with quarterpel precision require a
|
|
few extra bits to code, but the candidate vectors do not always
|
|
give (much) better results.
|
|
Quite often, the codec still spends bits on the extra precision,
|
|
but little or no extra quality is gained in return.
|
|
Unfortunately, there is no way to foresee the possible gains of
|
|
<option>qpel</option>, so you need to actually encode with and
|
|
without it to know for sure.
|
|
</para><para>
|
|
<option>qpel</option> can be almost double encoding time, and
|
|
requires as much as 25% more processing power to decode.
|
|
It is not supported by all standalone players.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">gmc</emphasis>
|
|
Tries to save bits on panning scenes by using a single motion
|
|
vector for the whole frame.
|
|
This almost always raises PSNR, but significantly slows down
|
|
encoding (as well as decoding).
|
|
Therefore, you should only use it when you have turned
|
|
<option>vhq</option> to the maximum.
|
|
<systemitem class="library">XviD</systemitem>'s GMC is more
|
|
sophisticated than DivX's, but is only supported by few
|
|
standalone players.
|
|
</para></listitem>
|
|
|
|
</itemizedlist>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-xvid-encoding-profiles">
|
|
<title>Encoding profiles</title>
|
|
<para>
|
|
XviD supports encoding profiles through the <option>profile</option> option,
|
|
which are used to impose restrictions on the properties of the XviD video
|
|
stream such that it will be playable on anything which supports the
|
|
chosen profile.
|
|
The restrictions relate to resolutions, bitrates and certain MPEG-4
|
|
features.
|
|
The following table shows what each profile supports.
|
|
</para>
|
|
<informaltable>
|
|
<tgroup cols="16" align="center">
|
|
<colspec colnum="1" colname="col1"/>
|
|
<colspec colnum="2" colname="col2"/>
|
|
<colspec colnum="3" colname="col3"/>
|
|
<colspec colnum="4" colname="col4"/>
|
|
<colspec colnum="5" colname="col5"/>
|
|
<colspec colnum="6" colname="col6"/>
|
|
<colspec colnum="7" colname="col7"/>
|
|
<colspec colnum="8" colname="col8"/>
|
|
<colspec colnum="9" colname="col9"/>
|
|
<colspec colnum="10" colname="col10"/>
|
|
<colspec colnum="11" colname="col11"/>
|
|
<colspec colnum="12" colname="col12"/>
|
|
<colspec colnum="13" colname="col13"/>
|
|
<colspec colnum="14" colname="col14"/>
|
|
<colspec colnum="15" colname="col15"/>
|
|
<colspec colnum="16" colname="col16"/>
|
|
<colspec colnum="17" colname="col17"/>
|
|
<spanspec spanname="spa2-5" namest="col2" nameend="col5"/>
|
|
<spanspec spanname="spa6-11" namest="col6" nameend="col11"/>
|
|
<spanspec spanname="spa12-17" namest="col12" nameend="col17"/>
|
|
<tbody>
|
|
<row>
|
|
<entry></entry>
|
|
<entry spanname="spa2-5">Simple</entry>
|
|
<entry spanname="spa6-11">Advanced Simple</entry>
|
|
<entry spanname="spa12-17">DivX</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Profile name</entry>
|
|
<entry>0</entry>
|
|
<entry>1</entry>
|
|
<entry>2</entry>
|
|
<entry>3</entry>
|
|
<entry>0</entry>
|
|
<entry>1</entry>
|
|
<entry>2</entry>
|
|
<entry>3</entry>
|
|
<entry>4</entry>
|
|
<entry>5</entry>
|
|
<entry>Handheld</entry>
|
|
<entry>Portable NTSC</entry>
|
|
<entry>Portable PAL</entry>
|
|
<entry>Home Theater NTSC</entry>
|
|
<entry>Home Theater PAL</entry>
|
|
<entry>HDTV</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Width [pixels]</entry>
|
|
<entry>176</entry>
|
|
<entry>176</entry>
|
|
<entry>352</entry>
|
|
<entry>352</entry>
|
|
<entry>176</entry>
|
|
<entry>176</entry>
|
|
<entry>352</entry>
|
|
<entry>352</entry>
|
|
<entry>352</entry>
|
|
<entry>720</entry>
|
|
<entry>176</entry>
|
|
<entry>352</entry>
|
|
<entry>352</entry>
|
|
<entry>720</entry>
|
|
<entry>720</entry>
|
|
<entry>1280</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Height [pixels]</entry>
|
|
<entry>144</entry>
|
|
<entry>144</entry>
|
|
<entry>288</entry>
|
|
<entry>288</entry>
|
|
<entry>144</entry>
|
|
<entry>144</entry>
|
|
<entry>288</entry>
|
|
<entry>288</entry>
|
|
<entry>576</entry>
|
|
<entry>576</entry>
|
|
<entry>144</entry>
|
|
<entry>240</entry>
|
|
<entry>288</entry>
|
|
<entry>480</entry>
|
|
<entry>576</entry>
|
|
<entry>720</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Frame rate [fps]</entry>
|
|
<entry>15</entry>
|
|
<entry>15</entry>
|
|
<entry>15</entry>
|
|
<entry>15</entry>
|
|
<entry>30</entry>
|
|
<entry>30</entry>
|
|
<entry>15</entry>
|
|
<entry>30</entry>
|
|
<entry>30</entry>
|
|
<entry>30</entry>
|
|
<entry>15</entry>
|
|
<entry>30</entry>
|
|
<entry>25</entry>
|
|
<entry>30</entry>
|
|
<entry>25</entry>
|
|
<entry>30</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Max average bitrate [kbps]</entry>
|
|
<entry>64</entry>
|
|
<entry>64</entry>
|
|
<entry>128</entry>
|
|
<entry>384</entry>
|
|
<entry>128</entry>
|
|
<entry>128</entry>
|
|
<entry>384</entry>
|
|
<entry>768</entry>
|
|
<entry>3000</entry>
|
|
<entry>8000</entry>
|
|
<entry>537.6</entry>
|
|
<entry>4854</entry>
|
|
<entry>4854</entry>
|
|
<entry>4854</entry>
|
|
<entry>4854</entry>
|
|
<entry>9708.4</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Peak average bitrate over 3 secs [kbps]</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>800</entry>
|
|
<entry>8000</entry>
|
|
<entry>8000</entry>
|
|
<entry>8000</entry>
|
|
<entry>8000</entry>
|
|
<entry>16000</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Max. B-frames</entry>
|
|
<entry>0</entry>
|
|
<entry>0</entry>
|
|
<entry>0</entry>
|
|
<entry>0</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>0</entry>
|
|
<entry>1</entry>
|
|
<entry>1</entry>
|
|
<entry>1</entry>
|
|
<entry>1</entry>
|
|
<entry>2</entry>
|
|
</row>
|
|
<row>
|
|
<entry>MPEG quantization</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>Adaptive quantization</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Interlaced encoding</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Quaterpixel</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
<row>
|
|
<entry>Global motion compensation</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry>X</entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
<entry></entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-xvid-example-settings">
|
|
<title>Encoding setting examples</title>
|
|
|
|
<para>
|
|
The following settings are examples of different encoding
|
|
option combinations that affect the speed vs quality tradeoff
|
|
at the same target bitrate.
|
|
</para>
|
|
|
|
<para>
|
|
All the encoding settings were tested on a 720x448 @30000/1001 fps
|
|
video sample, the target bitrate was 900kbps, and the machine was an
|
|
AMD-64 3400+ at 2400 Mhz in 64 bits mode.
|
|
Each encoding setting features the measured encoding speed (in
|
|
frames per second) and the PSNR loss (in dB) compared to the "very
|
|
high quality" setting.
|
|
Please understand that depending on your source, your machine type
|
|
and development advancements, you may get very different results.
|
|
</para>
|
|
|
|
<para>
|
|
<informaltable frame="all">
|
|
<tgroup cols="4">
|
|
<thead>
|
|
<row><entry>Description</entry><entry>Encoding options</entry><entry>speed (in fps)</entry><entry>Relative PSNR loss (in dB)</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>Very high quality</entry>
|
|
<entry><option>chroma_opt:vhq=4:bvhq=1:quant_type=mpeg</option></entry>
|
|
<entry>16fps</entry>
|
|
<entry>0dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>High quality</entry>
|
|
<entry><option>vhq=2:bvhq=1:chroma_opt:quant_type=mpeg</option></entry>
|
|
<entry>18fps</entry>
|
|
<entry>-0.1dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Fast</entry>
|
|
<entry><option>turbo:vhq=0</option></entry>
|
|
<entry>28fps</entry>
|
|
<entry>-0.69dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Realtime</entry>
|
|
<entry><option>turbo:nochroma_me:notrellis:max_bframes=0:vhq=0</option></entry>
|
|
<entry>38fps</entry>
|
|
<entry>-1.48dB</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
</para>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="menc-feat-x264">
|
|
<title>Encoding with the <systemitem class="library">x264</systemitem> codec</title>
|
|
<para>
|
|
<systemitem class="library">x264</systemitem> is a free library for
|
|
encoding H.264/AVC video streams.
|
|
Before starting to encode, you need to <link linkend="codec-x264-encode">
|
|
set up <application>MEncoder</application> to support it</link>.
|
|
</para>
|
|
|
|
<sect2 id="menc-feat-x264-encoding-options">
|
|
<title>Encoding options of x264</title>
|
|
|
|
<para>
|
|
Please begin by reviewing the
|
|
<systemitem class="library">x264</systemitem> section of
|
|
<application>MPlayer</application>'s man page.
|
|
This section is intended to be a supplement to the man page.
|
|
Here you will find quick hints about which options are most
|
|
likely to interest most people. The man page is more terse,
|
|
but also more exhaustive, and it sometimes offers much better
|
|
technical detail.
|
|
</para>
|
|
|
|
<sect3 id="menc-feat-x264-encoding-options-intro">
|
|
<title>Introduction</title>
|
|
<para>This guide considers two major categories of encoding options:</para>
|
|
|
|
<orderedlist>
|
|
<listitem><para>Options which mainly trade off encoding time vs. quality
|
|
</para></listitem>
|
|
<listitem><para>Options which may be useful for fulfilling various personal
|
|
preferences and special requirements</para></listitem>
|
|
</orderedlist>
|
|
|
|
<para>
|
|
Ultimately, only you can decide which options are best for your
|
|
purposes. The decision for the first class of options is the simplest:
|
|
you only have to decide whether you think the quality differences
|
|
justify the speed differences. For the second class of options,
|
|
preferences may be far more subjective, and more factors may be
|
|
involved. Note that some of the "personal preferences and special
|
|
requirements" options can still have large impacts on speed or quality,
|
|
but that is not what they are primarily useful for. A couple of the
|
|
"personal preference" options may even cause changes that look better
|
|
to some people, but look worse to others.
|
|
</para>
|
|
|
|
<para>
|
|
Before continuing, you need to understand that this guide uses only one
|
|
quality metric: global PSNR.
|
|
For a brief explanation of what PSNR is, see
|
|
<ulink url="http://en.wikipedia.org/wiki/PSNR">the Wikipedia article on PSNR</ulink>.
|
|
Global PSNR is the last PSNR number reported when you include
|
|
the <option>psnr</option> option in <option>x264encopts</option>.
|
|
Any time you read a claim about PSNR, one of the assumptions
|
|
behind the claim is that equal bitrates are used.
|
|
</para>
|
|
|
|
<para>
|
|
Nearly all of this guide's comments assume you are using
|
|
two pass.
|
|
When comparing options, there are two major reasons for using
|
|
two pass encoding.
|
|
First, using two pass often gains around 1dB PSNR, which is a
|
|
very big difference.
|
|
Secondly, testing options by doing direct quality comparisons
|
|
with one pass encodes introduces a major confounding
|
|
factor: bitrate often varies significantly with each encode.
|
|
It is not always easy to tell whether quality changes are due
|
|
mainly to changed options, or if they mostly reflect essentially
|
|
random differences in the achieved bitrate.
|
|
</para>
|
|
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-x264-encoding-options-speedvquality">
|
|
<title>Options which primarily affect speed and quality</title>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
<emphasis role="bold">subq</emphasis>:
|
|
Of the options which allow you to trade off speed for quality,
|
|
<option>subq</option> and <option>frameref</option> (see below) are usually
|
|
by far the most important.
|
|
If you are interested in tweaking either speed or quality, these
|
|
are the first options you should consider.
|
|
On the speed dimension, the <option>frameref</option> and
|
|
<option>subq</option> options interact with each other fairly
|
|
strongly.
|
|
Experience shows that, with one reference frame,
|
|
<option>subq=5</option> (the default setting) takes about 35% more time than
|
|
<option>subq=1</option>.
|
|
With 6 reference frames, the penalty grows to over 60%.
|
|
<option>subq</option>'s effect on PSNR seems fairly constant
|
|
regardless of the number of reference frames.
|
|
Typically, <option>subq=5</option> achieves 0.2-0.5 dB higher global
|
|
PSNR in comparison <option>subq=1</option>.
|
|
This is usually enough to be visible.
|
|
</para>
|
|
<para>
|
|
<option>subq=6</option> is the slowest, highest quality mode.
|
|
In comparison to <option>subq=5</option>, it usually gains 0.1-0.4 dB
|
|
global PSNR with speed costs varying from 25%-100%.
|
|
Unlike other levels of <option>subq</option>, the behavior of
|
|
<option>subq=6</option> does not depend much on <option>frameref</option>
|
|
and <option>me</option>. Instead, the effectiveness of <option>subq=6
|
|
</option> depends mostly upon the number of B-frames used. In normal
|
|
usage, this means <option>subq=6</option> has a large impact on both speed
|
|
and quality in complex, high motion scenes, but it may not have much effect
|
|
in low-motion scenes. Note that it is still recommended to always set
|
|
<option>bframes</option> to something other than zero (see below).
|
|
</para></listitem>
|
|
<listitem><para>
|
|
<emphasis role="bold">frameref</emphasis>:
|
|
<option>frameref</option> is set to 1 by default, but this
|
|
should not be taken to imply that it is reasonable to set it
|
|
to 1.
|
|
Merely raising <option>frameref</option> to 2 gains around
|
|
0.15dB PSNR with a 5-10% speed penalty; this seems like a
|
|
good tradeoff.
|
|
<option>frameref=3</option> gains around 0.25dB PSNR over
|
|
<option>frameref=1</option>, which should be a visible
|
|
difference.
|
|
<option>frameref=3</option> is around 15% slower than
|
|
<option>frameref=1</option>.
|
|
Unfortunately, diminishing returns set in rapidly.
|
|
<option>frameref=6</option> can be expected to gain only
|
|
0.05-0.1 dB over <option>frameref=3</option> at an additional
|
|
15% speed penalty.
|
|
Above <option>frameref=6</option>, the quality gains are
|
|
usually very small (although you should keep in mind throughout
|
|
this whole discussion that it can vary quite a lot depending on
|
|
your source).
|
|
In a fairly typical case, <option>frameref=12</option>
|
|
will improve global PSNR by a tiny 0.02dB over
|
|
<option>frameref=6</option>, at a speed cost of 15%-20%.
|
|
At such high <option>frameref</option> values, the only really
|
|
good thing that can be said is that increasing it even further will
|
|
almost certainly never <emphasis role="bold">harm</emphasis>
|
|
PSNR, but the additional quality benefits are barely even
|
|
measurable, let alone perceptible.
|
|
</para>
|
|
<note><title>Note:</title>
|
|
<para>
|
|
Raising <option>frameref</option> to unnecessarily high values
|
|
<emphasis role="bold">can</emphasis> and
|
|
<emphasis role="bold">usually does</emphasis>
|
|
hurt coding efficiency if you turn CABAC off.
|
|
With CABAC on (the default behavior), the possibility of setting
|
|
<option>frameref</option> "too high" currently seems too remote
|
|
to even worry about, and in the future, optimizations may remove
|
|
the possibility altogether.
|
|
</para>
|
|
</note>
|
|
<para>
|
|
If you care about speed, a reasonable compromise is to use low
|
|
<option>subq</option> and <option>frameref</option> values on
|
|
the first pass, and then raise them on the second pass.
|
|
Typically, this has a negligible negative effect on the final
|
|
quality: You will probably lose well under 0.1dB PSNR, which
|
|
should be much too small of a difference to see.
|
|
However, different values of <option>frameref</option> can
|
|
occasionally affect frametype decision.
|
|
Most likely, these are rare outlying cases, but if you want to
|
|
be pretty sure, consider whether your video has either
|
|
fullscreen repetitive flashing patterns or very large temporary
|
|
occlusions which might force an I-frame.
|
|
Adjust the first-pass <option>frameref</option> so it is large
|
|
enough to contain the duration of the flashing cycle (or occlusion).
|
|
For example, if the scene flashes back and forth between two images
|
|
over a duration of three frames, set the first pass
|
|
<option>frameref</option> to 3 or higher.
|
|
This issue is probably extremely rare in live action video material,
|
|
but it does sometimes come up in video game captures.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">me</emphasis>:
|
|
This option is for choosing the motion estimation search method.
|
|
Altering this option provides a straightforward quality-vs-speed
|
|
tradeoff. <option>me=1</option> is only a few percent faster than
|
|
the default search, at a cost of under 0.1dB global PSNR. The
|
|
default setting (<option>me=2</option>) is a reasonable tradeoff
|
|
between speed and quality. <option>me=3</option> gains a little under
|
|
0.1dB global PSNR, with a speed penalty that varies depending on
|
|
<option>frameref</option>. At high values of
|
|
<option>frameref</option> (e.g. 12 or so), <option>me=3</option>
|
|
is about 40% slower than the default <option> me=2</option>. With
|
|
<option>frameref=3</option>, the speed penalty incurred drops to
|
|
25%-30%.
|
|
</para>
|
|
<para>
|
|
<option>me=4</option> uses an exhaustive search that is too slow for
|
|
practical use.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">4x4mv</emphasis>:
|
|
This option enables the use of 8x4, 4x8 and 4x4 subpartitions in
|
|
predicted macroblocks. Enabling it results in a fairly consistent
|
|
10%-15% loss of speed. This option is rather useless in source
|
|
containing only low motion, however in some high-motion source,
|
|
particularly source with lots of small moving objects, gains of
|
|
about 0.1dB can be expected.
|
|
</para>
|
|
</listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">bframes</emphasis>:
|
|
If you are used to encoding with other codecs, you may have found
|
|
that B-frames are not always useful.
|
|
In H.264, this has changed: there are new techniques and block
|
|
types that are possible in B-frames.
|
|
Usually, even a naive B-frame choice algorithm can have a
|
|
significant PSNR benefit.
|
|
It is interesting to note that using B-frames usually speeds up
|
|
the second pass somewhat, and may also speed up a single
|
|
pass encode if adaptive B-frame decision is turned off.
|
|
</para>
|
|
<para>
|
|
With adaptive B-frame decision turned off
|
|
(<option>x264encopts</option>'s <option>nob_adapt</option>),
|
|
the optimal value for this setting is usually no more than
|
|
<option>bframes=1</option>, or else high-motion scenes can suffer.
|
|
With adaptive B-frame decision on (the default behavior), it is
|
|
safe to use higher values; the encoder will reduce the use of
|
|
B-frames in scenes where they would hurt compression.
|
|
The encoder rarely chooses to use more than 3 or 4 B-frames;
|
|
setting this option any higher will have little effect.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">b_adapt</emphasis>:
|
|
Note: This is on by default.
|
|
</para>
|
|
<para>
|
|
With this option enabled, the encoder will use a reasonably fast
|
|
decision process to reduce the number of B-frames used in scenes that
|
|
might not benefit from them as much.
|
|
You can use <option>b_bias</option> to tweak how B-frame-happy
|
|
the encoder is.
|
|
The speed penalty of adaptive B-frames is currently rather modest,
|
|
but so is the potential quality gain.
|
|
It usually does not hurt, however.
|
|
Note that this only affects speed and frametype decision on the
|
|
first pass.
|
|
<option>b_adapt</option> and <option>b_bias</option> have no
|
|
effect on subsequent passes.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">b_pyramid</emphasis>:
|
|
You might as well enable this option if you are using >=2 B-frames;
|
|
as the man page says, you get a little quality improvement at no
|
|
speed cost.
|
|
Note that these videos cannot be read by libavcodec-based decoders
|
|
older than about March 5, 2005.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">weight_b</emphasis>:
|
|
In typical cases, there is not much gain with this option.
|
|
However, in crossfades or fade-to-black scenes, weighted
|
|
prediction gives rather large bitrate savings.
|
|
In MPEG-4 ASP, a fade-to-black is usually best coded as a series
|
|
of expensive I-frames; using weighted prediction in B-frames
|
|
makes it possible to turn at least some of these into much smaller
|
|
B-frames.
|
|
Encoding time cost is minimal, as no extra decisions need to be made.
|
|
Also, contrary to what some people seem to guess, the decoder
|
|
CPU requirements are not much affected by weighted prediction,
|
|
all else being equal.
|
|
</para>
|
|
<para>
|
|
Unfortunately, the current adaptive B-frame decision algorithm
|
|
has a strong tendency to avoid B-frames during fades.
|
|
Until this changes, it may be a good idea to add
|
|
<option>nob_adapt</option> to your x264encopts, if you expect
|
|
fades to have a large effect in your particular video
|
|
clip.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-x264-encoding-options-misc-preferences">
|
|
<title>Options pertaining to miscellaneous preferences</title>
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
<emphasis role="bold">Two pass encoding</emphasis>:
|
|
Above, it was suggested to always use two pass encoding, but there
|
|
are still reasons for not using it. For instance, if you are capturing
|
|
live TV and encoding in realtime, you are forced to use single-pass.
|
|
Also, one pass is obviously faster than two passes; if you use the
|
|
exact same set of options on both passes, two pass encoding is almost
|
|
twice as slow.
|
|
</para>
|
|
<para>
|
|
Still, there are very good reasons for using two pass encoding. For
|
|
one thing, single pass ratecontrol is not psychic, and it often makes
|
|
unreasonable choices because it cannot see the big picture. For example,
|
|
suppose you have a two minute long video consisting of two distinct
|
|
halves. The first half is a very high-motion scene lasting 60 seconds
|
|
which, in isolation, requires about 2500kbps in order to look decent.
|
|
Immediately following it is a much less demanding 60-second scene
|
|
that looks good at 300kbps. Suppose you ask for 1400kbps on the theory
|
|
that this is enough to accomodate both scenes. Single pass ratecontrol
|
|
will make a couple of "mistakes" in such a case. First of all, it
|
|
will target 1400kbps in both segments. The first segment may end up
|
|
heavily overquantized, causing it to look unacceptably and unreasonably
|
|
blocky. The second segment will be heavily underquantized; it may look
|
|
perfect, but the bitrate cost of that perfection will be completely
|
|
unreasonable. What is even harder to avoid is the problem at the
|
|
transition between the two scenes. The first seconds of the low motion
|
|
half will be hugely over-quantized, because the ratecontrol is still
|
|
expecting the kind of bitrate requirements it met in the first half
|
|
of the video. This "error period" of heavily over-quantized low motion
|
|
will look jarringly bad, and will actually use less than the 300kbps
|
|
it would have taken to make it look decent. There are ways to
|
|
mitigate the pitfalls of single-pass encoding, but they may tend to
|
|
increase bitrate misprediction.
|
|
</para>
|
|
<para>
|
|
Multipass ratecontrol can offer huge advantages over a single pass.
|
|
Using the statistics gathered from the first pass encode, the encoder
|
|
can estimate, with reasonable accuracy, the "cost" (in bits) of
|
|
encoding any given frame, at any given quantizer. This allows for
|
|
a much more rational, better planned allocation of bits between the
|
|
expensive (high-motion) and cheap (low-motion) scenes. See
|
|
<option>qcomp</option> below for some ideas on how to tweak this
|
|
allocation to your liking.
|
|
</para>
|
|
<para>
|
|
Moreover, two passes need not take twice as long as one pass. You can
|
|
tweak the options in the first pass for higher speed and lower quality.
|
|
If you choose your options well, you can get a very fast first pass.
|
|
The resulting quality in the second pass will be slightly lower because size
|
|
prediction is less accurate, but the quality difference is normally much
|
|
too small to be visible. Try, for example, adding
|
|
<option>subq=1:frameref=1</option> to the first pass
|
|
<option>x264encopts</option>. Then, on the second pass, use slower,
|
|
higher-quality options:
|
|
<option>subq=6:frameref=15:4x4mv:me=3</option>
|
|
</para></listitem>
|
|
<listitem><para>
|
|
<emphasis role="bold">Three pass encoding</emphasis>?
|
|
|
|
x264 offers the ability to make an arbitrary number of consecutive
|
|
passes. If you specify <option>pass=1</option> on the first pass,
|
|
then use <option>pass=3</option> on a subsequent pass, the subsequent
|
|
pass will both read the statistics from the previous pass, and write
|
|
its own statistics. An additional pass following this one will have
|
|
a very good base from which to make highly accurate predictions of
|
|
framesizes at a chosen quantizer. In practice, the overall quality
|
|
gain from this is usually close to zero, and quite possibly a third
|
|
pass will result in slightly worse global PSNR than the pass before
|
|
it. In typical usage, three passes help if you get either bad bitrate
|
|
prediction or bad looking scene transitions when using only two passes.
|
|
This is somewhat likely to happen on extremely short clips. There are
|
|
also a few special cases in which three (or more) passes are handy
|
|
for advanced users, but for brevity, this guide omits discussing those
|
|
special cases.
|
|
|
|
</para></listitem>
|
|
<listitem><para>
|
|
<emphasis role="bold">qcomp</emphasis>:
|
|
<option>qcomp</option> trades off the number of bits allocated
|
|
to "expensive" high-motion versus "cheap" low-motion frames. At
|
|
one extreme, <option>qcomp=0</option> aims for true constant
|
|
bitrate. Typically this would make high-motion scenes look completely
|
|
awful, while low-motion scenes would probably look absolutely
|
|
perfect, but would also use many times more bitrate than they
|
|
would need in order to look merely excellent. At the other extreme,
|
|
<option>qcomp=1</option> achieves nearly constant quantization parameter
|
|
(QP). Constant QP does not look bad, but most people think it is more
|
|
reasonable to shave some bitrate off of the extremely expensive scenes
|
|
(where the loss of quality is not as noticeable) and reallocate it to
|
|
the scenes that are easier to encode at excellent quality.
|
|
<option>qcomp</option> is set to 0.6 by default, which may be slightly
|
|
low for many peoples' taste (0.7-0.8 are also commonly used).
|
|
</para></listitem>
|
|
<listitem><para>
|
|
<emphasis role="bold">keyint</emphasis>:
|
|
<option>keyint</option> is solely for trading off file seekability against
|
|
coding efficiency. By default, <option>keyint</option> is set to 250. In
|
|
25fps material, this guarantees the ability to seek to within 10 seconds
|
|
precision. If you think it would be important and useful to be able to
|
|
seek within 5 seconds of precision, set <option>keyint=125</option>;
|
|
this will hurt quality/bitrate slightly. If you care only about quality
|
|
and not about seekability, you can set it to much higher values
|
|
(understanding that there are diminishing returns which may become
|
|
vanishingly low, or even zero). The video stream will still have seekable
|
|
points as long as there are some scene changes.
|
|
</para></listitem>
|
|
<listitem><para>
|
|
<emphasis role="bold">deblockalpha, deblockbeta</emphasis>:
|
|
This topic is going to be a bit controversial.
|
|
</para>
|
|
<para>
|
|
H.264 defines a simple deblocking procedure on I-blocks that uses
|
|
pre-set strengths and thresholds depending on the QP of the block
|
|
in question.
|
|
By default, high QP blocks are filtered heavily, and low QP blocks
|
|
are not deblocked at all.
|
|
The pre-set strengths defined by the standard are well-chosen and
|
|
the odds are very good that they are PSNR-optimal for whatever
|
|
video you are trying to encode.
|
|
The <option>deblockalpha</option> and <option>deblockbeta</option>
|
|
parameters allow you to specify offsets to the preset deblocking
|
|
thresholds.
|
|
</para>
|
|
<para>
|
|
Many people seem to think it is a good idea to lower the deblocking
|
|
filter strength by large amounts (say, -3).
|
|
This is however almost never a good idea, and in most cases,
|
|
people who are doing this do not understand very well how
|
|
deblocking works by default.
|
|
</para>
|
|
<para>
|
|
The first and most important thing to know about the in-loop
|
|
deblocking filter is that the default thresholds are almost always
|
|
PSNR-optimal.
|
|
In the rare cases that they are not optimal, the ideal offset is
|
|
plus or minus 1.
|
|
Adjusting deblocking parameters by a larger amount is almost
|
|
guaranteed to hurt PSNR.
|
|
Strengthening the filter will smear more details; weakening the
|
|
filter will increase the appearance of blockiness.
|
|
</para>
|
|
<para>
|
|
It is definitely a bad idea to lower the deblocking thresholds if
|
|
your source is mainly low in spacial complexity (i.e., not a lot
|
|
of detail or noise).
|
|
The in-loop filter does a rather excellent job of concealing
|
|
the artifacts that occur.
|
|
If the source is high in spacial complexity, however, artifacts
|
|
are less noticeable.
|
|
This is because the ringing tends to look like detail or noise.
|
|
Human visual perception easily notices when detail is removed,
|
|
but it does not so easily notice when the noise is wrongly
|
|
represented.
|
|
When it comes to subjective quality, noise and detail are somewhat
|
|
interchangeable.
|
|
By lowering the deblocking filter strength, you are most likely
|
|
increasing error by adding ringing artifacts, but the eye does
|
|
not notice because it confuses the artifacts with detail.
|
|
</para>
|
|
|
|
<para>
|
|
This <emphasis role="bold">still</emphasis> does not justify
|
|
lowering the deblocking filter strength, however.
|
|
You can generally get better quality noise from postprocessing.
|
|
If your H.264 encodes look too blurry or smeared, try playing with
|
|
<option>-vf noise</option> when you play your encoded movie.
|
|
<option>-vf noise=8a:4a</option> should conceal most mild
|
|
artifacting.
|
|
It will almost certainly look better than the results you
|
|
would have gotten just by fiddling with the deblocking filter.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-x264-example-settings">
|
|
<title>Encoding setting examples</title>
|
|
|
|
<para>
|
|
The following settings are examples of different encoding
|
|
option combinations that affect the speed vs quality tradeoff
|
|
at the same target bitrate.
|
|
</para>
|
|
|
|
<para>
|
|
All the encoding settings were tested on a 720x448 @30000/1001 fps
|
|
video sample, the target bitrate was 900kbps, and the machine was an
|
|
AMD-64 3400+ at 2400 Mhz in 64 bits mode.
|
|
Each encoding setting features the measured encoding speed (in
|
|
frames per second) and the PSNR loss (in dB) compared to the "very
|
|
high quality" setting.
|
|
Please understand that depending on your source, your machine type
|
|
and development advancements, you may get very different results.
|
|
</para>
|
|
|
|
<para>
|
|
<informaltable frame="all">
|
|
<tgroup cols="4">
|
|
<thead>
|
|
<row><entry>Description</entry><entry>Encoding options</entry><entry>speed (in fps)</entry><entry>Relative PSNR loss (in dB)</entry></row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>Very high quality</entry>
|
|
<entry><option>subq=6:4x4mv:8x8dct:me=3:frameref=5:bframes=3:b_pyramid:weight_b</option></entry>
|
|
<entry>6fps</entry>
|
|
<entry>0dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>High quality</entry>
|
|
<entry><option>subq=5:4x4mv:8x8dct:frameref=2:bframes=3:b_pyramid:weight_b</option></entry>
|
|
<entry>13fps</entry>
|
|
<entry>-0.89dB</entry>
|
|
</row>
|
|
<row>
|
|
<entry>Fast</entry>
|
|
<entry><option>subq=4:bframes=2:b_pyramid:weight_b</option></entry>
|
|
<entry>17fps</entry>
|
|
<entry>-1.48dB</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
</para>
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
<sect1 id="menc-feat-vcd-dvd">
|
|
<title>Using MEncoder to create VCD/SVCD/DVD-compliant files.</title>
|
|
|
|
<sect2 id="menc-feat-vcd-dvd-constraints">
|
|
<title>Format Constraints</title>
|
|
<para>
|
|
<application>MEncoder</application> is capable of creating VCD, SCVD
|
|
and DVD format MPEG files using the
|
|
<systemitem class="library">libavcodec</systemitem> library.
|
|
These files can then be used in conjunction with
|
|
<ulink url="http://www.gnu.org/software/vcdimager/vcdimager.html">vcdimager</ulink>
|
|
or
|
|
<ulink url="http://dvdauthor.sourceforge.net/">dvdauthor</ulink>
|
|
to create discs that will play on a standard set-top player.
|
|
</para>
|
|
|
|
<para>
|
|
The DVD, SVCD, and VCD formats are subject to heavy constraints.
|
|
Only a small selection of encoded picture sizes and aspect ratios are
|
|
available.
|
|
If your movie does not already meet these requirements, you may have
|
|
to scale,crop or add black borders to the picture to make it
|
|
compliant.
|
|
</para>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-constraints-resolution">
|
|
<title>Format Constraints</title>
|
|
|
|
<informaltable frame="all">
|
|
<tgroup cols="9">
|
|
<thead>
|
|
<row>
|
|
<entry>Format</entry>
|
|
<entry>Resolution</entry>
|
|
<entry>V. Codec</entry>
|
|
<entry>V. Bitrate</entry>
|
|
<entry>Sample Rate</entry>
|
|
<entry>A. Codec</entry>
|
|
<entry>A. Bitrate</entry>
|
|
<entry>FPS</entry>
|
|
<entry>Aspect</entry>
|
|
</row>
|
|
</thead>
|
|
<tbody>
|
|
<row>
|
|
<entry>NTSC DVD</entry>
|
|
<entry>720x480, 704x480, 352x480, 352x240</entry>
|
|
<entry>MPEG-2</entry>
|
|
<entry>9800 kbps</entry>
|
|
<entry>48000 Hz</entry>
|
|
<entry>AC3,PCM</entry>
|
|
<entry>1536 kbps (max)</entry>
|
|
<entry>30000/1001, 24000/1001</entry>
|
|
<entry>4:3, 16:9 (only for 720x480)</entry>
|
|
</row>
|
|
<row>
|
|
<entry>NTSC DVD</entry>
|
|
<entry>352x240<footnote id='fn-rare-resolutions'><para>
|
|
These resolutions are rarely used for DVDs because
|
|
they are fairly low quality.</para></footnote></entry>
|
|
<entry>MPEG-1</entry>
|
|
<entry>1856 kbps</entry>
|
|
<entry>48000 Hz</entry>
|
|
<entry>AC3,PCM</entry>
|
|
<entry>1536 kbps (max)</entry>
|
|
<entry>30000/1001, 24000/1001</entry>
|
|
<entry>4:3, 16:9</entry>
|
|
</row>
|
|
<row>
|
|
<entry>NTSC SVCD</entry>
|
|
<entry>480x480</entry>
|
|
<entry>MPEG-2</entry>
|
|
<entry>2600 kbps</entry>
|
|
<entry>44100 Hz</entry>
|
|
<entry>MP2</entry>
|
|
<entry>384 kbps (max)</entry>
|
|
<entry>30000/1001</entry>
|
|
<entry>4:3</entry>
|
|
</row>
|
|
<row>
|
|
<entry>NTSC VCD</entry>
|
|
<entry>352x240</entry>
|
|
<entry>MPEG-1</entry>
|
|
<entry>1150 kbps</entry>
|
|
<entry>44100 Hz</entry>
|
|
<entry>MP2</entry>
|
|
<entry>224 kbps</entry>
|
|
<entry>24000/1001, 30000/1001</entry>
|
|
<entry>4:3</entry>
|
|
</row>
|
|
<row>
|
|
<entry>PAL DVD</entry>
|
|
<entry>720x576, 704x576, 352x576, 352x288</entry>
|
|
<entry>MPEG-2</entry>
|
|
<entry>9800 kbps</entry>
|
|
<entry>48000 Hz</entry>
|
|
<entry>MP2,AC3,PCM</entry>
|
|
<entry>1536 kbps (max)</entry>
|
|
<entry>25</entry>
|
|
<entry>4:3, 16:9 (only for 720x576)</entry>
|
|
</row>
|
|
<row>
|
|
<entry>PAL DVD</entry>
|
|
<entry>352x288<footnoteref linkend='fn-rare-resolutions'/></entry>
|
|
<entry>MPEG-1</entry>
|
|
<entry>1856 kbps</entry>
|
|
<entry>48000 Hz</entry>
|
|
<entry>MP2,AC3,PCM</entry>
|
|
<entry>1536 kbps (max)</entry>
|
|
<entry>25</entry>
|
|
<entry>4:3, 16:9</entry>
|
|
</row>
|
|
<row>
|
|
<entry>PAL SVCD</entry>
|
|
<entry>480x576</entry>
|
|
<entry>MPEG-2</entry>
|
|
<entry>2600 kbps</entry>
|
|
<entry>44100 Hz</entry>
|
|
<entry>MP2</entry>
|
|
<entry>384 kbps (max)</entry>
|
|
<entry>25</entry>
|
|
<entry>4:3</entry>
|
|
</row>
|
|
<row>
|
|
<entry>PAL VCD</entry>
|
|
<entry>352x288</entry>
|
|
<entry>MPEG-1</entry>
|
|
<entry>1152 kbps</entry>
|
|
<entry>44100 Hz</entry>
|
|
<entry>MP2</entry>
|
|
<entry>224 kbps</entry>
|
|
<entry>25</entry>
|
|
<entry>4:3</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</informaltable>
|
|
|
|
<para>
|
|
If your movie has 2.35:1 aspect (most recent action movies), you will
|
|
have to add black borders or crop the movie down to 16:9 to make a DVD
|
|
or VCD.
|
|
If you add black borders, try to align them at 16-pixel boundaries in
|
|
order to minimize the impact on encoding performance.
|
|
Thankfully DVD has sufficiently excessive bitrate that you do not have
|
|
to worry too much about encoding efficiency, but SVCD and VCD are
|
|
highly bitrate-starved and require effort to obtain acceptable quality.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-constraints-gop">
|
|
<title>GOP Size Constraints</title>
|
|
<para>
|
|
DVD, VCD, and SVCD also constrain you to relatively low
|
|
GOP (Group of Pictures) sizes.
|
|
For 30 fps material the largest allowed GOP size is 18.
|
|
For 25 or 24 fps, the maximum is 15.
|
|
The GOP size is set using the <option>keyint</option> option.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-constraints-bitrate">
|
|
<title>Bitrate Constraints</title>
|
|
<para>
|
|
VCD video is required to be CBR at 1152 kbps.
|
|
This highly limiting constraint also comes along with an extremly low vbv
|
|
buffer size of 327 kilobits.
|
|
SVCD allows varying video bitrates up to 2500 kbps, and a somewhat less
|
|
restrictive vbv buffer size of 917 kilobits is allowed.
|
|
DVD video bitrates may range anywhere up to 9800 kbps (though typical
|
|
bitrates are about half that), and the vbv buffer size is 1835 kilobits.
|
|
</para>
|
|
</sect3>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-vcd-dvd-output">
|
|
<title>Output Options</title>
|
|
<para>
|
|
<application>MEncoder</application> has options to control the output
|
|
format.
|
|
Using these options we can instruct it to create the correct type of
|
|
file.
|
|
</para>
|
|
|
|
<para>
|
|
The options for VCD and SVCD are called xvcd and xsvcd, because they
|
|
are extended formats.
|
|
They are not strictly compliant, mainly because the output does not
|
|
contain scan offsets.
|
|
If you need to generate an SVCD image, you should pass the output file
|
|
to
|
|
<ulink url="http://www.gnu.org/software/vcdimager/vcdimager.html">vcdimager</ulink>.
|
|
</para>
|
|
|
|
<para>
|
|
VCD:
|
|
<screen>
|
|
-of mpeg -mpegopts format=xvcd
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
SVCD:
|
|
<screen>
|
|
-of mpeg -mpegopts format=xsvcd
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
DVD:
|
|
<screen>
|
|
-of mpeg -mpegopts format=dvd
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
DVD with NTSC Pullup:
|
|
<screen>
|
|
-of mpeg -mpegopts format=dvd:telecine -ofps 24000/1001
|
|
</screen>
|
|
This allows 24000/1001 fps progressive content to be encoded at 30000/1001
|
|
fps whilst maintaing DVD-compliance.
|
|
</para>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-output-aspect">
|
|
<title>Aspect Ratio</title>
|
|
<para>
|
|
The aspect argument of <option>-lavcopts</option> is used to encode
|
|
the aspect ratio of the file.
|
|
During playback the aspect ratio is used to restore the video to the
|
|
correct size.
|
|
</para>
|
|
|
|
<para>
|
|
16:9 or "Widescreen"
|
|
<screen>
|
|
-lavcopts aspect=16/9
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
4:3 or "Fullscreen"
|
|
<screen>
|
|
-lavcopts aspect=4/3
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
2.35:1 or "Cinemascope" NTSC
|
|
<screen>
|
|
-vf scale=720:368,expand=720:480 -lavcopts aspect=16/9
|
|
</screen>
|
|
To calculate the correct scaling size, use the expanded NTSC width of
|
|
854/2.35 = 368
|
|
</para>
|
|
|
|
<para>
|
|
2.35:1 or "Cinemascope" PAL
|
|
<screen>
|
|
-vf scale="720:432,expand=720:576 -lavcopts aspect=16/9
|
|
</screen>
|
|
To calculate the correct scaling size, use the expanded PAL width of
|
|
1024/2.35 = 432
|
|
</para>
|
|
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-output-srate">
|
|
<title>Sample Rate Conversion</title>
|
|
<para>
|
|
If the audio sample rate in the original file is not the same as
|
|
required by the target format, sample rate conversion is required.
|
|
This is achieved using the <option>-srate</option> option and
|
|
the <option>-af lavcresample</option> audio filter together.
|
|
</para>
|
|
<para>
|
|
DVD:
|
|
<screen>
|
|
-srate 48000 -af lavcresample=48000
|
|
</screen>
|
|
</para>
|
|
<para>
|
|
VCD and SVCD:
|
|
<screen>
|
|
-srate 44100 -af lavcresample=44100
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-vcd-dvd-lavc">
|
|
<title>Using libavcodec for VCD/SVCD/DVD Encoding</title>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-lavc-intro">
|
|
<title>Introduction</title>
|
|
<para>
|
|
<systemitem class="library">libavcodec</systemitem> can be used to
|
|
create VCD/SVCD/DVD compliant video by using the appropriate options.
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-lavc-options">
|
|
<title>lavcopts</title>
|
|
<para>
|
|
This is a list of fields in <option>-lavcopts</option> that you may
|
|
be required to change in order to make a complaint movie for VCD, SVCD,
|
|
or DVD:
|
|
</para>
|
|
|
|
<itemizedlist>
|
|
<listitem><para>
|
|
<emphasis role="bold">acodec</emphasis>:
|
|
<option>mp2</option> for VCD, SVCD, or PAL DVD;
|
|
<option>ac3</option> is most commonly used for DVD.
|
|
PCM audio may also be used for DVD, but this is mostly a big waste of
|
|
space.
|
|
Note that MP3 audio is not compliant for any of these formats, but
|
|
players often have no problem playing it anyway.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">abitrate</emphasis>:
|
|
224 for VCD; up to 384 for SVCD; up to 1536 for DVD, but commonly
|
|
used values range from 192 kbps for stereo to 384 kbps for 5.1 channel
|
|
sound.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vcodec</emphasis>:
|
|
<option>mpeg1video</option> for VCD;
|
|
<option>mpeg2video</option> for SVCD;
|
|
<option>mpeg2video</option> is usually used for DVD but you may also use
|
|
<option>mpeg1video</option> for CIF resolutions.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">keyint</emphasis>:
|
|
Used to set the GOP size.
|
|
18 for 30fps material, or 15 for 25/24 fps material.
|
|
Commercial producers seem to prefer keyframe intervals of 12.
|
|
It is possible to make this much larger and still retain compatibility
|
|
with most players.
|
|
A <option>keyint</option> of 25 should never cause any problems.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vrc_buf_size</emphasis>:
|
|
327 for VCD, 917 for SVCD, and 1835 for DVD.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vrc_minrate</emphasis>:
|
|
1152, for VCD. May be left alone for SVCD and DVD.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vrc_maxrate</emphasis>:
|
|
1152 for VCD; 2500 for SVCD; 9800 for DVD.
|
|
For SVCD and DVD, you might wish to use lower values depending on your
|
|
own personal preferences and requirements.
|
|
</para></listitem>
|
|
|
|
<listitem><para>
|
|
<emphasis role="bold">vbitrate</emphasis>:
|
|
1152 for VCD;
|
|
up to 2500 for SVCD;
|
|
up to 9800 for DVD.
|
|
For the latter two formats, vbitrate should be set based on personal
|
|
preference.
|
|
For instance, if you insist on fitting 20 or so hours on a DVD, you
|
|
could use vbitrate=400.
|
|
The resulting video quality would probably be quite bad.
|
|
If you are trying to squeeze out the maximum possible quality on a DVD,
|
|
use vbitrate=9800, but be warned that this could constrain you to less
|
|
than an hour of video on a single-layer DVD.
|
|
</para></listitem>
|
|
</itemizedlist>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-lavc-examples">
|
|
<title>Examples</title>
|
|
<para>
|
|
This is a typical minimum set of <option>-lavcopts</option> for
|
|
encoding video:
|
|
</para>
|
|
<para>
|
|
VCD:
|
|
<screen>
|
|
-lavcopts vcodec=mpeg1video:vrc_buf_size=327:vrc_minrate=1152:\
|
|
vrc_maxrate=1152:vbitrate=1152:keyint=15:acodec=mp2
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
SVCD:
|
|
<screen>
|
|
-lavcopts vcodec=mpeg2video:vrc_buf_size=917:vrc_maxrate=2500:vbitrate=1800:\
|
|
keyint=15:acodec=mp2
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
DVD:
|
|
<screen>
|
|
-lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:\
|
|
keyint=15:acodec=ac3
|
|
</screen>
|
|
</para>
|
|
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-lavc-advanced">
|
|
<title>Advanced Options</title>
|
|
<para>
|
|
For higher quality encoding, you may also wish to add quality-enhancing
|
|
options to lavcopts, such as <option>trell</option>,
|
|
<option>mbd=2</option>, and others.
|
|
Note that <option>qpel</option> and <option>v4mv</option>, while often
|
|
useful with MPEG-4, are not usable with MPEG-1 or MPEG-2.
|
|
Also, if you are trying to make a very high quality DVD encode, it may
|
|
be useful to add <option>dc=10</option> to lavcopts.
|
|
Doing so may help reduce the appearance of blocks in flat-colored areas.
|
|
Putting it all together, this is an example of a set of lavcopts for a
|
|
higher quality DVD:
|
|
</para>
|
|
|
|
<para>
|
|
<screen>
|
|
-lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=8000:\
|
|
keyint=15:trell:mbd=2:precmp=2:subcmp=2:cmp=2:dia=-10:predia=-10:cbp:mv0:\
|
|
vqmin=1:lmin=1:dc=10
|
|
</screen>
|
|
</para>
|
|
|
|
</sect3>
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-vcd-dvd-audio">
|
|
<title>Encoding Audio</title>
|
|
<para>
|
|
VCD and SVCD support MPEG-1 layer II audio, using one of
|
|
<systemitem class="library">toolame</systemitem>,
|
|
<systemitem class="library">twolame</systemitem>,
|
|
or <systemitem class="library">libavcodec</systemitem>'s MP2 encoder.
|
|
The libavcodec MP2 is far from being as good as the other two libraries,
|
|
however it should always be available to use.
|
|
VCD only supports constant bitrate audio (CBR) whereas SVCD supports
|
|
variable bitrate (VBR), too.
|
|
Be careful when using VBR because some bad standalone players might not
|
|
support it too well.
|
|
</para>
|
|
|
|
<para>
|
|
For DVD audio, <systemitem class="library">libavcodec</systemitem>'s
|
|
AC3 codec is used.
|
|
</para>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-audio-toolame">
|
|
<title>toolame</title>
|
|
<para>
|
|
For VCD and SVCD:
|
|
<screen>
|
|
-oac toolame -toolameopts br=224
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-audio-twolame">
|
|
<title>twolame</title>
|
|
<para>
|
|
For VCD and SVCD:
|
|
<screen>
|
|
-oac twolame -twolameopts br=224
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-audio-lavc">
|
|
<title>libavcodec</title>
|
|
<para>
|
|
For DVD with 2 channel sound:
|
|
<screen>
|
|
-oac lavc -lavcopts acodec=ac3:abitrate=192
|
|
</screen>
|
|
</para>
|
|
<para>
|
|
For DVD with 5.1 channel sound:
|
|
<screen>
|
|
-channels 6 -oac lavc -lavcopts acodec=ac3:abitrate=384
|
|
</screen>
|
|
</para>
|
|
<para>
|
|
For VCD and SVCD:
|
|
<screen>
|
|
-oac lavc -lavcopts acodec=mp2:abitrate=224
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
</sect2>
|
|
|
|
<sect2 id="menc-feat-vcd-dvd-all">
|
|
<title>Putting it all Together</title>
|
|
<para>
|
|
This section shows some complete commands for creating VCD/SVCD/DVD
|
|
compliant videos.
|
|
</para>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-pal-dvd">
|
|
<title>PAL DVD</title>
|
|
<para>
|
|
<screen>
|
|
mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd -vf scale=720:576,\
|
|
harddup -srate 48000 -af lavcresample=48000 -lavcopts vcodec=mpeg2video:\
|
|
vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:keyint=15:acodec=ac3:\
|
|
abitrate=192:aspect=16/9 -ofps 25 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-ntsc-dvd">
|
|
<title>NTSC DVD</title>
|
|
<para>
|
|
<screen>
|
|
mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=dvd -vf scale=720:480,\
|
|
harddup -srate 48000 -af lavcresample=48000 -lavcopts vcodec=mpeg2video:\
|
|
vrc_buf_size=1835:vrc_maxrate=9800:vbitrate=5000:keyint=18:acodec=ac3:\
|
|
abitrate=192:aspect=16/9 -ofps 30000/1001 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-pal-ac3-copy">
|
|
<title>PAL AVI Containing AC3 Audio to DVD</title>
|
|
<para>
|
|
If the source already has AC3 audio, use -oac copy instead of re-encoding it.
|
|
<screen>
|
|
mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd -vf scale=720:576,\
|
|
harddup -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:vrc_maxrate=9800:\
|
|
vbitrate=5000:keyint=15:aspect=16/9 -ofps 25 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-ntsc-ac3-copy">
|
|
<title>NTSC AVI Containing AC3 Audio to DVD</title>
|
|
<para>
|
|
If the source already has AC3 audio, and is NTSC @ 24000/1001 fps:
|
|
<screen>
|
|
mencoder -oac copy -ovc lavc -of mpeg -mpegopts format=dvd:telecine \
|
|
-vf scale=720:480,harddup -lavcopts vcodec=mpeg2video:vrc_buf_size=1835:\
|
|
vrc_maxrate=9800:vbitrate=5000:keyint=15:aspect=16/9 -ofps 24000/1001 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-pal-svcd">
|
|
<title>PAL SVCD</title>
|
|
<para>
|
|
<screen>
|
|
mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd -vf \
|
|
scale=480:576,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
|
|
vcodec=mpeg2video:mbd=2:keyint=15:vrc_buf_size=917:vrc_minrate=600:\
|
|
vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224 -ofps 25 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-ntsc-svcd">
|
|
<title>NTSC SVCD</title>
|
|
<para>
|
|
<screen>
|
|
mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xsvcd -vf \
|
|
scale=480:480,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
|
|
vcodec=mpeg2video:mbd=2:keyint=18:vrc_buf_size=917:vrc_minrate=600:\
|
|
vbitrate=2500:vrc_maxrate=2500:acodec=mp2:abitrate=224 -ofps 30000/1001 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-pal-vcd">
|
|
<title>PAL VCD</title>
|
|
<para>
|
|
<screen>
|
|
mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
|
|
scale=352:288,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
|
|
vcodec=mpeg1video:keyint=15:vrc_buf_size=327:vrc_minrate=1152:vbitrate=1152:\
|
|
vrc_maxrate=1152:acodec=mp2:abitrate=224 -ofps 25 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
<sect3 id="menc-feat-vcd-dvd-all-ntsc-vcd">
|
|
<title>NTSC VCD</title>
|
|
<para>
|
|
<screen>
|
|
mencoder -oac lavc -ovc lavc -of mpeg -mpegopts format=xvcd -vf \
|
|
scale=352:240,harddup -srate 44100 -af lavcresample=44100 -lavcopts \
|
|
vcodec=mpeg1video:keyint=18:vrc_buf_size=327:vrc_minrate=1152:vbitrate=1152:\
|
|
vrc_maxrate=1152:acodec=mp2:abitrate=224 -ofps 30000/1001 \
|
|
-o <replaceable>movie.mpg</replaceable> <replaceable>movie.avi</replaceable>
|
|
</screen>
|
|
</para>
|
|
</sect3>
|
|
|
|
</sect2>
|
|
|
|
</sect1>
|
|
|
|
</chapter>
|