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Moves the "audio" section just before the "muxing" section. + fixes suggested by Jeff 

git-svn-id: svn://svn.mplayerhq.hu/mplayer/trunk@16087 b3059339-0415-0410-9bf9-f77b7e298cf2
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gpoirier 2005-07-24 21:37:24 +00:00
parent 323d7eb108
commit 97e333bf0d
1 changed files with 76 additions and 74 deletions
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150
DOCS/xml/en/encoding-guide.xml
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@ -972,7 +972,7 @@
change the bitrate as well!.
</para>
<para>
Bitrate does <emphasis role="bold">not</emphasis> scale proportional
Bitrate does <emphasis role="bold">not</emphasis> scale proportionally
to resolution.
That is to say, a 320x240 file at 200 kbit/sec will not be the same
quality as the same movie at 640x480 and 800 kbit/sec!
@ -1010,7 +1010,7 @@
rigor.
Further, given that movies vary greatly with regard to noise, detail,
degree of motion, etc., it's futile to make general recommendations
for bits per length-of-diagonal (the analogue of bits per pixel,
for bits per length-of-diagonal (the analog of bits per pixel,
using the square root).
</para>
<para>
@ -1082,70 +1082,39 @@
</sect2>
<sect2 id="menc-feat-dvd-mpeg4-audio">
<title>Audio</title>
<sect2 id="menc-feat-dvd-mpeg4-filtering">
<title>Filtering</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).
In general, you want to do as little filtering as possible to the movie
in order to remain close to the original DVD source. Cropping is often
necessary (as described above), but avoid to scale the video. Although
scaling down is sometimes preferred to using higher quantizers, we want
to avoid both these things: remember that we decided from the start to
trade bits for quality.
</para>
<para>
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.
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>
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.
One thing you might want to do, however, is pass the video through a
very light denoise filter, such as <option>-vf hqdn3d=2:1:2</option>.
Again, it is a matter of putting those bits to better use: why waste them
encoding noise when you can just add that noise back in during playback?
Increasing the parameters for <option>hqdn3d</option> will further
improve compressibility, but if you increase the values too much, you
risk degrading the image visibily. The suggested values above
(<option>2:1:2</option>) are quite conservative; you should feel free to
experiment with higher values and observe the results for yourself.
</para>
</sect2>
<sect2 id="menc-feat-dvd-mpeg4-interlacing">
<title>Interlacing and Telecine</title>
@ -1254,34 +1223,67 @@ Note the <option>ilmv</option> and <option>ildct</option> options.
</para>
</sect2>
<sect2 id="menc-feat-dvd-mpeg4-filtering">
<title>Filtering</title>
<sect2 id="menc-feat-dvd-mpeg4-audio">
<title>Audio</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.
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>
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.
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>
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.
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>