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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision$ -->
<chapter id="mencoder">
<title>Encoding with <application>MEncoder</application></title>
<para>
For the complete list of available <application>MEncoder</application> options
and examples, please see the man page. For a series of hands-on examples and
detailed guides on using several encoding parameters, read the
<ulink url="../../tech/encoding-tips.txt">encoding-tips</ulink> that were
collected from several mailing list threads on MPlayer-users. Search the
<ulink url="http://mplayerhq.hu/pipermail/mplayer-users/">archives</ulink>
for a wealth of discussions about all aspects of and problems related to
encoding with <application>MEncoder</application>.
</para>
<sect1 id="menc-feat-mpeg4">
<title>Encoding two pass MPEG-4 (&quot;DivX&quot;)</title>
<para>
The name comes from the fact that this method encodes the file <emphasis>twice</emphasis>.
The first encoding (dubbed pass) creates some temporary files
(<filename>*.log</filename>) with a size of few megabytes, do not delete
them yet (you can delete the AVI). In the second pass, the two pass output
file is created, using the bitrate data from the temporary files. The
resulting file will have much better image quality. If this is the first
time you heard about this, you should consult some guides available on the
net.
</para>
<example>
<title>copy audio track</title>
<para>
Two pass encode of a DVD to an MPEG-4 (&quot;DivX&quot;) AVI while copying
the audio track.
<screen>
mencoder dvd://2 -ovc lavc -lavcopts vcodec=mpeg4:vpass=1 -oac copy -o <replaceable>movie.avi</replaceable>
mencoder dvd://2 -ovc lavc -lavcopts vcodec=mpeg4:vpass=2 -oac copy -o <replaceable>movie.avi</replaceable>
</screen>
</para>
</example>
<example>
<title>encode audio track</title>
<para>
Two pass encode of a DVD to an MPEG-4 (&quot;DivX&quot;) AVI while encoding
the audio track to MP3.
<screen>
mencoder dvd://2 -ovc lavc -lavcopts vcodec=mpeg4:vpass=1 -oac mp3lame -lameopts vbr=3 -o <replaceable>movie.avi</replaceable>
mencoder dvd://2 -ovc lavc -lavcopts vcodec=mpeg4:vpass=2 -oac mp3lame -lameopts vbr=3 -o <replaceable>movie.avi</replaceable>
</screen>
</para>
</example>
</sect1>
<sect1 id="menc-feat-mpeg">
<title>Encoding to MPEG format</title>
<para>
<application>MEncoder</application> can create MPEG (MPEG-PS) format output
files. It is probably useful only with
<link linkend="ffmpeg"><systemitem class="library">libavcodec</systemitem></link>'s
<emphasis>mpeg1video</emphasis> codec, because players - except
<application>MPlayer</application> - expect MPEG-1 video, and MPEG-1 layer 2 (MP2)
audio streams in MPEG files.
</para>
<para>
This feature is not very useful right now, aside that it probably has many bugs,
but the more importantly because <application>MEncoder</application> currently
cannot encode MPEG-1 layer 2 (MP2) audio, which all other players expect in MPEG files.
</para>
<para>
To change <application>MEncoder</application>'s output file format,
use the <option>-of mpeg</option> option.
</para>
<para>
Example:
<screen>
mencoder -of mpeg -ovc lavc -lavcopts vcodec=mpeg1video -oac copy <replaceable>other_options</replaceable> <replaceable>media.avi</replaceable> -o <replaceable>output.mpg</replaceable>
</screen>
</para>
</sect1>
<sect1 id="menc-feat-rescale">
<title>Rescaling movies</title>
<para>
Often the need to resize movie images' size emerges. Its reasons can be
many: decreasing file size, network bandwidth,etc. Most people even do
rescaling when converting DVDs or SVCDs to DivX AVI. If you wish to rescale,
read the <link linkend="aspect">Preserving aspect ratio</link> section.
</para>
<para>
The scaling process is handled by the <literal>scale</literal> video filter:
<option>-vf scale=<replaceable>width</replaceable>:<replaceable>height</replaceable></option>.
Its quality can be set with the <option>-sws</option> option.
If it is not specified, <application>MEncoder</application> will use 2: bicubic.
</para>
<para>
Usage:
<screen>
mencoder <replaceable>input.mpg</replaceable> -ovc lavc -lavcopts vcodec=mpeg4 -vf scale=640:480 -o <replaceable>output.avi</replaceable>
</screen>
</para>
</sect1>
<sect1 id="menc-feat-streamcopy">
<title>Stream copying</title>
<para>
<application>MEncoder</application> can handle input streams in two ways:
<emphasis role="bold">encode</emphasis> or <emphasis role="bold">copy</emphasis>
them. This section is about <emphasis role="bold">copying</emphasis>.
</para>
<itemizedlist>
<listitem><para>
<emphasis role="bold">Video stream</emphasis> (option <option>-ovc copy</option>):
nice stuff can be done :) Like, putting (not converting!) FLI or VIVO or
MPEG-1 video into an AVI file! Of course only
<application>MPlayer</application> can play such files :) And it probably
has no real life value at all. Rationally: video stream copying can be
useful for example when only the audio stream has to be encoded (like,
uncompressed PCM to MP3).
</para></listitem>
<listitem><para>
<emphasis role="bold">Audio stream</emphasis> (option <option>-oac copy</option>):
straightforward. It is possible to take an external audio file (MP3,
WAV) and mux it into the output stream. Use the
<option>-audiofile <replaceable>filename</replaceable></option> option
for this.
</para></listitem>
</itemizedlist>
</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):
<informaltable frame="all">
<tgroup cols="2">
<thead>
<row><entry>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>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>
an old RealVideo codec
</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>
</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>
</sect1>
<sect1 id="menc-feat-enc-images">
<title>Encoding from multiple input image files (JPEG, PNG, TGA, SGI)</title>
<para>
<application>MEncoder</application> is capable of creating movies from one
or more JPEG, PNG or TGA files. With simple framecopy it can create MJPEG
(Motion JPEG), MPNG (Motion PNG) or MTGA (Motion TGA) files.
</para>
<orderedlist>
<title>Explanation of the process:</title>
<listitem><para>
<application>MEncoder</application> <emphasis>decodes</emphasis> the input image(s) with
<systemitem class="library">libjpeg</systemitem> (when decoding PNGs, it
will use <systemitem class="library">libpng</systemitem>).
</para></listitem>
<listitem><para>
<application>MEncoder</application> then feeds the decoded image to the
chosen video compressor (DivX4, XviD, FFmpeg msmpeg4, etc.).
</para></listitem>
</orderedlist>
<formalpara>
<title>Examples</title>
<para>
The explanation of the <option>-mf</option> option is in the man page.
<informalexample>
<para>
Creating an MPEG-4 file from all the JPEG files in the current directory:
<screen>
mencoder mf://*.jpg -mf w=800:h=600:fps=25:type=jpg -ovc lavc -lavcopts vcodec=mpeg4 -oac copy -o <replaceable>output.avi</replaceable>
</screen>
</para>
</informalexample>
<informalexample>
<para>
Creating an MPEG-4 file from some JPEG files in the current directory:
<screen>
mencoder mf://<replaceable>frame001.jpg,frame002.jpg</replaceable> -mf w=800:h=600:fps=25:type=jpg -ovc lavc -lavcopts vcodec=mpeg4 -oac copy -o <replaceable>output.avi</replaceable>
</screen>
</para>
</informalexample>
<informalexample>
<para>
Creating a Motion JPEG (MJPEG) file from all the JPEG files in the current
directory:
<screen>
mencoder mf://*.jpg -mf w=800:h=600:fps=25:type=jpg -ovc copy -oac copy -o <replaceable>output.avi</replaceable>
</screen>
</para>
</informalexample>
<informalexample>
<para>
Creating an uncompressed file from all the PNG files in the current directory:
<screen>
mencoder mf:// -mf w=800:h=600:fps=25:type=png -ovc raw -oac copy -o <replaceable>output.avi</replaceable>
</screen>
</para>
</informalexample>
<note><para>
Width must be integer multiple of 4, it is a limitation of the RAW RGB AVI format.
</para></note>
<informalexample>
<para>
Creating a Motion PNG (MPNG) file from all the PNG files in the current
directory:
<screen>
mencoder mf://*.png -mf w=800:h=600:fps=25:type=png -ovc copy -oac copy -o <replaceable>output.avi</replaceable> <!--
--></screen>
</para>
</informalexample>
<informalexample>
<para>
Creating a Motion TGA (MTGA) file from all the TGA files in the current
directory:
<screen>
mencoder mf://*.tga -mf w=800:h=600:fps=25:type=tga -ovc copy -oac copy -o <replaceable>output.avi</replaceable><!--
--></screen>
</para>
</informalexample>
</para>
</formalpara>
</sect1>
<sect1 id="menc-feat-extractsub">
<title>Extracting DVD subtitles to VOBsub file</title>
<para>
<application>MEncoder</application> is capable of extracting subtitles from
a DVD into VOBsub formatted files. They consist of a pair of files ending in
<filename>.idx</filename> and <filename>.sub</filename> and are usually
packaged in a single <filename>.rar</filename> archive.
<application>MPlayer</application> can play these with the
<option>-vobsub</option> and <option>-vobsubid</option> options.
</para>
<para>
You specify the basename (i.e without the <filename>.idx</filename> or
<filename>.sub</filename> extension) of the output files with
<option>-vobsubout</option> and the index for this subtitle in the
resulting files with <option>-vobsuboutindex</option>.
</para>
<para>
If the input is not from a DVD you should use <option>-ifo</option> to
indicate the <filename>.ifo</filename> file needed to construct the
resulting <filename>.idx</filename> file.
</para>
<para>
If the input is not from a DVD and you do not have the
<filename>.ifo</filename> file you will need to use the
<option>-vobsubid</option> option to let it know what language id to put in
the <filename>.idx</filename> file.
</para>
<para>
Each run will append the running subtitle if the <filename>.idx</filename>
and <filename>.sub</filename> files already exist. So you should remove any
before starting.
</para>
<example>
<title>Copying two subtitles from a DVD while doing two pass encoding</title>
<screen>
rm subtitles.idx subtitles.sub
mencoder dvd://1 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vpass=1 -vobsubout subtitles -vobsuboutindex 0 -sid 2
mencoder dvd://1 -oac copy -ovc lavc -lavcopts vcodec=mpeg4:vpass=2 -vobsubout subtitles -vobsuboutindex 1 -sid 5<!--
--></screen>
</example>
<example>
<title>Copying a french subtitle from an MPEG file</title>
<screen>
rm subtitles.idx subtitles.sub
mencoder <replaceable>movie.mpg</replaceable> -ifo <replaceable>movie.ifo</replaceable> -vobsubout subtitles -vobsuboutindex 0 -vobsuboutid fr -sid 1<!--
--></screen>
</example>
</sect1>
<sect1 id="aspect">
<title>Preserving aspect ratio</title>
<para>
DVDs and SVCDs (i.e. MPEG-1/2) files contain an aspect ratio value, which
describes how the player should scale the video stream, so humans will not
have egg heads (ex.: 480x480 + 4:3 = 640x480). However when encoding to AVI
(DivX) files, you have be aware that AVI headers do not store this value.
Rescaling the movie is disgusting and time consuming, there has to be a better
way!
</para>
<para>There is</para>
<para>
MPEG-4 has an unique feature: the video stream can contain its needed aspect
ratio. Yes, just like MPEG-1/2 (DVD, SVCD) and H.263 files. Regretfully, there are
<emphasis role="bold">no</emphasis> video players outside which support this
attribute of MPEG-4, except <application>MPlayer</application>.
</para>
<para>
This feature can be used only with
<link linkend="ffmpeg"><systemitem class="library">libavcodec</systemitem></link>'s
<systemitem>mpeg4</systemitem> codec. Keep in mind: although
<application>MPlayer</application> will correctly play the created file,
other players will use the wrong aspect ratio.
</para>
<para>
You seriously should crop the black bands over and below the movie image.
See the man page for the usage of the <systemitem>cropdetect</systemitem> and
<systemitem>crop</systemitem> filters.
</para>
<para>
Usage
<screen>mencoder <replaceable>sample-svcd.mpg</replaceable> -ovc lavc -lavcopts vcodec=mpeg4:autoaspect -vf crop=714:548:0:14 -oac copy -o <replaceable>output.avi</replaceable></screen>
</para>
</sect1>
<sect1 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 &quot;Notch&quot; 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>
</sect1>
<sect1 id="menc-feat-dvd-mpeg4">
<title>Making a high quality MPEG-4 (&quot;DivX&quot;) rip of a DVD movie</title>
<para>
One frequently asked question is "How do I make the highest quality rip for
a given size?". Another question is "How do I make the highest quality DVD
rip possible? I do not care about file size, I just want the best quality."
</para>
<para>
The latter question is perhaps at least somewhat wrongly posed. After all, if
you do not care about file size, why not simply copy the entire MPEG-2 video
stream from the the DVD? Sure, your AVI will end up being 5GB, give
or take, but if you want the best quality and do not care about size,
this is certainly your best option.
</para>
<para>
In fact, the reason you want to transcode a DVD into MPEG-4 is
specifically because you <emphasis role="bold">do</emphasis> care about
file size.
</para>
<para>
It is difficult to offer a cookbook recipe on how to create a very high
quality DVD rip. There are several factors to consider, and you should
understand these details or else you are likely to end up disappointed
with your results. Below we will investigate some of these issues, and
then have a look at an example. We assume you are using
<systemitem class="library">libavcodec</systemitem> to encode the video,
although the theory applies to other codecs as well.
</para>
<para>
If this seems to be too much for you, you should probably use one of the
many fine frontends that are listed in the
<ulink url="http://mplayerhq.hu/homepage/design7/projects.html#mencoder_frontends">MEncoder section</ulink>
of our related projects page.
That way, you should be able to achieve high quality rips without too much
thinking, because most of those tools are designed to take clever decisions
for you.
</para>
<sect2 id="menc-feat-dvd-mpeg4-preparing-encode">
<title>Preparing to encode: Identifying source material and framerate</title>
<para>
Before you even think about encoding a movie, you need to take
several preliminary steps.
</para>
<para>
The first and most important step before you encode should be
determining what type of content you are dealing with.
If your source material comes from DVD or broadcast/cable/satellite
TV, it will be stored in one of two formats: NTSC for North
America and Japan, PAL for Europe, etc.
It is important to realize, however, that this is just the formatting for
presentation on a television, and often does
<emphasis role="bold">not</emphasis> correspond to the
original format of the movie.
In order to produce a suitable encode, you need to know the original
format.
Failure to take this into account will result in ugly combing
(interlacing) artifacts in your encode.
Besides being ugly, the artifacts also harm coding efficiency:
You will get worse quality per bitrate.
</para>
<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-fps">
<title>Identifying source framerate</title>
<para>
Here is a list of common types of source material, where you are
likely to find them, and their properties:
</para>
<itemizedlist>
<listitem><para>
<emphasis role="bold">Standard Film</emphasis>: Produced for
theatrical display at 24fps.
</para></listitem>
<listitem><para>
<emphasis role="bold">PAL video</emphasis>: Recorded with a PAL
video camera at 50 fields per second.
A field consists of just the odd- or even-numbered lines of a
frame.
Television was designed to refresh these in alternation as a
cheap form of analog compression.
The human eye supposedly compensates for this, but once you
understand interlacing you will learn to see it on TV too and
never enjoy TV again.
Two fields do <emphasis role="bold">not</emphasis> make a
complete frame, because they are captured 1/50 of a second apart
in time, and thus they do not line up unless there is no motion.
</para></listitem>
<listitem><para>
<emphasis role="bold">NTSC Video</emphasis>: Recorded with an
NTSC video camera at 59.94 fields per second, or 60 fields per
second in the pre-color era.
Otherwise similar to PAL.
</para></listitem>
<listitem><para>
<emphasis role="bold">Animation</emphasis>: Usually drawn at
24fps, but also comes in mixed-framerate varieties.
</para></listitem>
<listitem><para>
<emphasis role="bold">Computer Graphics (CG)</emphasis>: Can be
any framerate, but some are more common than others; 23 and
30 frames per second are typical for NTSC, and 25fps is typical
for PAL.
</para></listitem>
<listitem><para>
<emphasis role="bold">Old Film</emphasis>: Various lower
framerates.
</para></listitem>
</itemizedlist>
</sect3>
<sect3 id="menc-feat-dvd-mpeg4-preparing-encode-material">
<title>Identifying source material</title>
<para>
Movies consisting of frames are referred to as progressive,
while those consisting of independent fields are called
either interlaced or video - though this latter term is
ambiguous.
</para>
<para>
To further complicate matters, some movies will be a mix of
several of the above.
</para>
<para>
The most important distinction to make between all of these
formats is that some are frame-based, while others are
field-based.
<emphasis role="bold">Whenever</emphasis> a movie is prepared
for display on television (including DVD), it is converted to a
field-based format.
The various methods by which this can be done are collectively
referred to as "pulldown", of which the infamous NTSC
"3:2 telecine" is one variety.
Unless the original material was also field-based (and the same
fieldrate), you are getting the movie in a format other than the
original.
</para>
<itemizedlist>
<title>There are several common types of pulldown:</title>
<listitem><para>
<emphasis role="bold">PAL 2:2 pulldown</emphasis>: The nicest of
them all.
Each frame is shown for the duration of two fields, by extracting the
even and odd lines and showing them in alternation.
If the original material is 24fps, this process speeds up the
movie by 4%.
</para></listitem>
<listitem><para>
<emphasis role="bold">PAL 2:2:2:2:2:2:2:2:2:2:2:3 pulldown</emphasis>:
Every 12th frame is shown for the duration of three fields, instead of
just two.
This avoids the 4% speedup issue, but makes the process much
more difficult to reverse.
It is usually seen in musical productions where adjusting the
speed by 4% would seriously damage the musical score.
</para></listitem>
<listitem><para>
<emphasis role="bold">NTSC 3:2 telecine</emphasis>: Frames are
shown alternately for the duration of 3 fields or 2 fields.
This gives a fieldrate 2.5 times the original framerate.
The result is also slowed down very slightly from 60 fields per
second to 59.94 fields per second to maintain NTSC fieldrate.
</para></listitem>
<listitem><para>
<emphasis role="bold">NTSC 2:2 pulldown</emphasis>: Used for
showing 30fps material on NTSC.
Nice, just like 2:2 PAL pulldown.
</para></listitem>
</itemizedlist>
<para>
There are also methods for converting between NTSC and PAL video,
but such topics are beyond the scope of this guide.
If you encounter such a movie and want to encode it, your best
bet is to find a copy in the original format.
Conversion between these two formats is highly destructive and
cannot be reversed cleanly, so your encode will greatly suffer
if it is made from a converted source.
</para>
<para>
When video is stored on DVD, consecutive pairs of fields are
grouped as a frame, even though they are not intended to be shown
at the same moment in time.
The MPEG-2 standard used on DVD and digital TV provides both a
way to encode the original progressive frames, and store in
the header of each frame the number of fields for which it should
be shown.
If this method has been used, the movie will often be described
as "soft-telecined", since the process only directs the
DVD player to apply pulldown to the movie rather than altering
the movie itself.
This case is highly preferable since it can easily be reversed
(actually ignored) by the encoder, and since it preserves maximal
quality.
However, many DVD and broadcast production studios do not use
proper encoding techniques but instead produce movies with
"hard telecine", where fields are actually duplicated in the
encoded MPEG-2.
</para>
<para>
The procedures for dealing with these cases will be covered later
in this guide.
For now, we leave you with some guides to identifying which type
of material you are dealing with:
</para>
<itemizedlist>
<title>NTSC regions:</title>
<listitem><para>
If <application>MPlayer</application> prints that the framerate
has changed to 23.976 when watching your movie, and never changes
back, it is almost certainly 24fps content that has been
"soft telecined".
</para></listitem>
<listitem><para>
If <application>MPlayer</application> shows the framerate
switching back and forth between 23.976 and 29.97, and you see
"combing" at times, then there are several possibilities.
The 23.976 fps segments are almost certainly 24fps progressive
content, "soft telecined", but the 29.97 fps parts could be
either hard-telecined 24fps content or NTSC video content.
Use the same guidelines as the following two cases to determine
which.
</para></listitem>
<listitem><para>
If <application>MPlayer</application> never shows the framerate
changing, and every single frame with motion appears combed, your
movie is NTSC video at 59.94 fields per second.
</para></listitem>
<listitem><para>
If <application>MPlayer</application> never shows the framerate
changing, and two frames out of every five appear combed, your
movie is "hard telecined" 24fps content.
</para></listitem>
</itemizedlist>
<itemizedlist>
<title>PAL regions:</title>
<listitem><para>
If you never see any combing, your movie is 2:2 pulldown.
</para></listitem>
<listitem><para>
If you see combing alternating in and out every half second,
then your movie is 2:2:2:2:2:2:2:2:2:2:2:3 pulldown.
</para></listitem>
<listitem><para>
If you always see combing during motion, then your movie is PAL
video at 50 fields per second.
</para></listitem>
</itemizedlist>
<note><title>Hint:</title>
<para>
<application>MPlayer</application> can slow down movie playback
with the -speed option.
Try using <option>-speed</option> 0.2 to watch the movie very
slowly and identify the pattern, if you cannot see it at full speed.
</para>
</note>
</sect3>
</sect2>
<sect2 id="menc-feat-dvd-mpeg4-2pass">
<title>Constant quantizer vs. multipass</title>
<para>
It is possible to encode your movie at a wide range of qualities.
With modern video encoders and a bit of pre-codec compression
(downscaling and denoising), it is possible to achieve very good
quality at 700 MB, for a 90-110 minute widescreen movie.
Furthermore, all but the longest movies can be encoded with near-perfect
quality at 1400 MB.
</para>
<para>
There are three approaches to encoding the video: constant bitrate
(CBR), constant quantizer, and multipass (ABR, or average bitrate).
</para>
<note><title>Note:</title>
<para>
Most codecs which support ABR encode only support two pass encode
while some others such as <systemitem class="library">x264</systemitem>
and <systemitem class="library">libavcodec</systemitem> support
multipass, which slightly improves quality at each pass,
yet this improvement is no longer mesurable nor noticeable after the
4th or so pass.
Therefore, in this section, two pass and multipass will be used
interchangeably.
</para>
</note>
<para>
In each of these modes, <systemitem class="library">libavcodec</systemitem>
breaks the video frame into 16x16 pixel macroblocks and then applies a
quantizer to each macroblock. The lower the quantizer, the better the
quality and higher the bitrate. The method
<systemitem class="library">libavcodec</systemitem> uses to determine
which quantizer to use for a given macroblock varies and is highly
tunable. (This is an extreme over-simplification of the actual
process, but the basic concept is useful to understand.)
</para>
<para>
When you specify a constant bitrate, <systemitem
class="library">libavcodec</systemitem> will encode the video, discarding
detail as much as necessary and as little as possible in order to remain
lower than the given bitrate. If you truly do not care about file size,
you could as well use CBR and specify a bitrate of infinity. (In
practice, this means a value high enough so that it poses no limit, like
10000Kbit.) With no real restriction on bitrate, the result is that
<systemitem class="library">libavcodec</systemitem> will use the lowest
possible quantizer for each macroblock (as specified by
<option>vqmin</option>, which is 2 by default). As soon as you specify a
low enough bitrate that <systemitem class="library">libavcodec</systemitem>
is forced to use a higher quantizer, then you are almost certainly ruining
the quality of your video.
In order to avoid that, you should probably downscale your video, according
to the method described later on in this guide.
In general, you should avoid CBR altogether if you care about quality.
</para>
<para>
With constant quantizer, <systemitem
class="library">libavcodec</systemitem> uses the same quantizer, as
specified by the <option>vqscale</option> option, on every macroblock. If
you want the highest quality rip possible, again ignoring bitrate, you can
use <option>vqscale=2</option>. This will yield the same bitrate and PSNR
(peak signal-to-noise ratio) as CBR with
<option>vbitrate</option>=infinity and the default <option>vqmin</option>
of 2.
</para>
<para>
The problem with constant quantizing is that it uses the given quantizer
whether the macroblock needs it or not. That is, it might be possible
to use a higher quantizer on a macroblock without sacrificing visual
quality. Why waste the bits on an unnecessarily low quantizer? Your
CPU has as many cycles as there is time, but there is only so many bits
on your hard disk.
</para>
<para>
With a two pass encode, the first pass will rip the movie as though it
were CBR, but it will keep a log of properties for each frame. This
data is then used during the second pass in order to make intelligent
decisions about which quantizers to use. During fast action or low
detail scenes, higher quantizers will likely be used, and during
slow moving or high detail scenes, lower quantizers will be used.
</para>
<para>
If you use <option>vqscale=2</option>, then you are wasting bits. If you
use <option>vqscale=3</option>, then you are not getting the highest
quality rip. Suppose you rip a DVD at <option>vqscale=3</option>, and
the result is 1800Kbit. If you do a two pass encode with
<option>vbitrate=1800</option>, the resulting video will have <emphasis
role="bold">higher quality</emphasis> for the
<emphasis role="bold">same bitrate</emphasis>.
</para>
<para>
Since you are now convinced that two pass is the way to go, the real
question now is what bitrate to use? The answer is that there is no
single answer. Ideally you want to choose a bitrate that yields the
best balance between quality and file size. This is going to vary
depending on the source video.
</para>
<para>
If size does not matter, a good starting point for a very high quality
rip is about 2000Kbit plus or minus 200Kbit.
For fast action or high detail source video, or if you just have a very
critical eye, you might decide on 2400 or 2600.
For some DVDs, you might not notice a difference at 1400Kbit. It is a
good idea to experiment with scenes at different bitrates to get a feel.
</para>
<para>
If you aim at a certain size, you will have to somehow calculate the bitrate.
But before that, you need to know how much space you should reserve for the
audio track(s), so you should <link linkend="menc-feat-dvd-mpeg4-audio">rip
those</link> first.
You can compute the bitrate with the following equation:
<systemitem>bitrate = (target_size_in_Mbytes - sound_size_in_Mbytes) *
1024 * 1024 / length_in_secs * 8 / 1000</systemitem>
For instance, to squeeze a two-hour movie onto a 702MB CD, with 60MB
of audio track, the video bitrate will have to be:
<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>
<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>
</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>
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-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 needn't worry
much about frame rate. 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 59.94 fields per second
is halved to 25 or 29.97 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
59.94 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:ilmv:ildct:acodec=mp2:abitrate=224
</screen>
<para>
Note the <option>ilmv</option> and <option>ildct</option> options.
</para>
</sect2>
<sect2 id="menc-feat-dvd-mpeg4-filtering">
<title>Filtering</title>
<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 do not 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-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 libavcodec does not yet support closed GOP (the option
<option>cgop</option> does not currently work), so DivX5 will not be able to
decode anything encoded with B-frames.
</para></listitem>
<listitem><para>
<emphasis role="bold">vb_strategy=1</emphasis>: helps in high-motion scenes.
Requires vmax_b_frames >= 2.
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 (+20% 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-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 needn't 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>
<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 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-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-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-intro">
<title>What options should I use to get the best results?</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.
</para>
<orderedlist>
<title>There are mainly three types of considerations when choosing encoding
options:</title>
<listitem><para>Trading off encoding time vs. quality</para></listitem>
<listitem><para>Frame type decision options</para></listitem>
<listitem><para>Ratecontrol and quantization decision options</para></listitem>
</orderedlist>
<para>
This guide is mostly concerned with the first class of options.
The other two types often have more to do with personal
preferences and individual requirements.
</para>
<para>
Before continuing, please note 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 is a dubious proposition because 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
differences in the achieved bitrate.
</para>
<para>
Of the options which allow you to trade off speed for quality,
<option>subq</option> and <option>frameref</option> 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.
</para>
<para>
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> 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> gains 0.2-0.5 dB
global PSNR over <option>subq=1</option>.
This is usually enough to be visible.
</para>
</sect2>
<sect2 id="menc-feat-x264-encoding-options">
<title>Encoding options of x264</title>
<itemizedlist>
<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 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">bframes</emphasis>:
The usefulness of B-frames is questionable in most other codecs
you may be used to.
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 also interesting to note that if you turn off the adaptive
B-frame decision (<option>nob_adapt</option>), encoding with
<option>bframes</option> usually speeds up encoding speed somewhat.
</para>
<para>
With adaptive B-frame decision turned off
(<option>x264encopts</option>'s <option>nob_adapt</option>),
the optimal value for this setting will usually range from
<option>bframes=1</option> to <option>bframes=3</option>.
With adaptive B-frame decision on (the default behavior), it is
probably safe to use higher values; the encoder will try to
reduce the use of B-frames in scenes where they would hurt
compression.
</para>
<para>
If you are going to use <option>bframes</option> at all, consider
setting the maximum number of B-frames to 2 or higher in order to
take advantage of weighted prediction.
</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 some simple
heuristics 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 more
reasonably-sized B-frames.
Encoding time cost seems to be minimal, if there is any.
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 significant effect in your particular video
clip.
</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>
</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
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 60000/10001 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
&quot;30000/1001 fps NTSC content.&quot;
</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
&quot;soft-telecine&quot; 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 &quot;blink&quot;: 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
&quot;hard-telecine&quot;. Since hard-telecine is already 60000/1001 fields
per second, the DVD player plays the video without any manipulation.
</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 &quot;combing&quot;) 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 &quot;mixed progressive and telecine&quot; 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 &quot;30000/1001 fps NTSC&quot;
and &quot;24000/1001 fps progressive NTSC&quot;. Watch the bottom of
<application>MPlayer</application>'s output to see these messages.
</para>
<para>
You should check the &quot;30000/1001 fps NTSC&quot; 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 &quot;mixed progressive and interlaced&quot; content, progressive
and interlaced video have been spliced together.
</para>
<para>
This category looks just like &quot;mixed progressive and telecine&quot;,
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 -nosound -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 &quot;guess&quot; 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 -nosound -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 &quot;deint&quot;), 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 -nosound -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 -nosound -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 -nosound -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
&quot;mixed progressive and telecine&quot;.
<screen>mencoder dvd://1 -nosound -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 -nosound -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 &amp; 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
&quot;jump back in time&quot; 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 (&quot;brightness&quot;) and chroma (&quot;color&quot;)
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>
</chapter>
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