faq.texi

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

\input texinfo @c -*- texinfo -*-

@settitle FFmpeg FAQ
@titlepage
@sp 7
@center @titlefont{FFmpeg FAQ}
@sp 3
@end titlepage


@chapter General Problems

@section I cannot read this file although this format seems to be supported by ffmpeg.

Even if ffmpeg can read the file format, it may not support all its
codecs. Please consult the supported codec list in the ffmpeg
documentation.

@section How do I encode single pictures to movies?

First, rename your pictures to follow a numerical sequence.
For example, img1.jpg, img2.jpg, img3.jpg,...
Then you may run:

@example
  ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
@end example

Notice that @samp{%d} is replaced by the image number.

@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...

The same logic is used for any image format that ffmpeg reads.

@section How do I encode movie to single pictures?

Use:

@example
  ffmpeg -i movie.mpg movie%d.jpg
@end example

The @file{movie.mpg} used as input will be converted to
@file{movie1.jpg}, @file{movie2.jpg}, etc...

Instead of relying on file format self-recognition, you may also use
@table @option
@item -vcodec ppm
@item -vcodec png
@item -vcodec mjpeg
@end table
to force the encoding.

Applying that to the previous example:
@example
  ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
@end example

Beware that there is no "jpeg" codec. Use "mjpeg" instead.

@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?

No. FFmpeg only supports open source codecs. Windows DLLs are not
portable, bloated and often slow.

@section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem?

This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work.

@section Why do I see a slight quality degradation with multithreaded MPEG* encoding?

For multithreaded MPEG* encoding, the encoded slices must be independent,
otherwise thread n would practically have to wait for n-1 to finish, so it's
quite logical that there is a small reduction of quality. This is not a bug.

@section How can I read from the standard input or write to the standard output?

Use @file{-} as filename.

@section Why does ffmpeg not decode audio in VOB files?

The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
as the component that handles AC3 decoding (liba52) is currently released under
the GPL. If you have liba52 installed on your system, enable AC3 decoding
with @code{./configure --enable-liba52 --enable-gpl}. Take care: by
enabling AC3, you automatically change the license of libavcodec from
LGPL to GPL.

@section Which codecs are supported by Windows?

Windows does not support standard formats like MPEG very well, unless you
install some additional codecs

The following list of video codecs should work on most Windows systems:
@table @option
@item msmpeg4v2
.avi/.asf
@item msmpeg4
.asf only
@item wmv1
.asf only
@item wmv2
.asf only
@item mpeg4
only if you have some MPEG-4 codec installed like ffdshow or XviD
@item mpeg1
.mpg only
@end table
Note, ASF files often have .wmv or .wma extensions in Windows. It should also
be mentioned that Microsoft claims a patent on the ASF format, and may sue
or threaten users who create ASF files with non-Microsoft software. It is
strongly advised to avoid ASF where possible.

The following list of audio codecs should work on most Windows systems:
@table @option
@item adpcm_ima_wav
@item adpcm_ms
@item pcm
@item mp3
if some MP3 codec like LAME is installed
@end table

@section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?

This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
(@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-420-2.4.26.patch?view=co}). This may also
apply cleanly to other 2.4-series kernels.

@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?

Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
will cause somewhat too strong filtering. A fix is to apply (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.4.26.patch?view=co})
or (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co})
and pass 'combfilter=2'.

@section I have a problem with an old version of ffmpeg; where should I report it?
Nowhere. Upgrade to the latest release or if there is no recent release upgrade
to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
become the first person in history to get an answer different from "upgrade
to Subversion HEAD".

@section -f jpeg doesn't work.

Try '-f image2 test%d.jpg'.

@section Why can I not change the framerate?

Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
Choose a different codec with the -vcodec command line option.

@section ffmpeg does not work; What is wrong?

Try a 'make distclean' in the ffmpeg source directory before the build. If this does not help see
(@url{http://ffmpeg.org/bugreports.html}).

@section How do I encode XviD or DivX video with ffmpeg?

Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
standard (note that there are many other coding formats that use this
same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
force the fourcc 'xvid' to be stored as the video fourcc rather than the
default.

@section How do I encode videos which play on the iPod?

@table @option
@item needed stuff
-acodec libfaac -vcodec mpeg4 width<=320 height<=240
@item working stuff
4mv, title
@item non-working stuff
B-frames
@item example command line
ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 320x180 -title X output.mp4
@end table

@section How do I encode videos which play on the PSP?

@table @option
@item needed stuff
-acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
@item working stuff
4mv, title
@item non-working stuff
B-frames
@item example command line
ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -ar 24000 -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp output.mp4
@item needed stuff for H.264
-acodec libfaac -vcodec h264 width*height<=76800 width%16=0? height%16=0? -ar 48000 -coder 1 -r 30000/1001 or 15000/1001 -f psp
@item working stuff for H.264
title, loop filter
@item non-working stuff for H.264
CAVLC
@item example command line
ffmpeg -i input -acodec libfaac -ab 128kb -vcodec h264 -b 1200kb -ar 48000 -mbd 2 -coder 1 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp -flags loop -trellis 2 -partitions parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 output.mp4
@end table

@section Which are good parameters for encoding high quality MPEG-4?

'-mbd rd -flags +4mv+trell+aic -cmp 2 -subcmp 2 -g 300 -pass 1/2',
things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.

@section Which are good parameters for encoding high quality MPEG-1/MPEG-2?

'-mbd rd -flags +trell -cmp 2 -subcmp 2 -g 100 -pass 1/2'
but beware the '-g 100' might cause problems with some decoders.
Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.

@section Interlaced video looks very bad when encoded with ffmpeg, whats wrong?

You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
material, and try '-top 0/1' if the result looks really messed-up.

@section How can I read DirectShow files?

If you have built FFmpeg with @code{./configure --enable-avisynth}
(only possible on MinGW/Cygwin platforms),
then you may use any file that DirectShow can read as input.
(Be aware that this feature has been recently added,
so you will need to help yourself in case of problems.)

Just create an "input.avs" text file with this single line ...
@example
  DirectShowSource("C:\path to your file\yourfile.asf")
@end example
... and then feed that text file to FFmpeg:
@example
  ffmpeg -i input.avs
@end example

For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.