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464 lines
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464 lines
18 KiB
\input texinfo @c -*- texinfo -*- |
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@settitle FFmpeg FAQ |
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@titlepage |
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@sp 7 |
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@center @titlefont{FFmpeg FAQ} |
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@sp 3 |
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@end titlepage |
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@chapter General Problems |
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@section I cannot read this file although this format seems to be supported by ffmpeg. |
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Even if ffmpeg can read the file format, it may not support all its |
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codecs. Please consult the supported codec list in the ffmpeg |
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documentation. |
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@section How do I encode single pictures to movies? |
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First, rename your pictures to follow a numerical sequence. |
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For example, img1.jpg, img2.jpg, img3.jpg,... |
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Then you may run: |
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@example |
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ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg |
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@end example |
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Notice that @samp{%d} is replaced by the image number. |
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@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc... |
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The same logic is used for any image format that ffmpeg reads. |
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@section How do I encode movie to single pictures? |
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Use: |
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@example |
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ffmpeg -i movie.mpg movie%d.jpg |
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@end example |
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The @file{movie.mpg} used as input will be converted to |
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@file{movie1.jpg}, @file{movie2.jpg}, etc... |
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Instead of relying on file format self-recognition, you may also use |
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@table @option |
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@item -vcodec ppm |
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@item -vcodec png |
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@item -vcodec mjpeg |
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@end table |
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to force the encoding. |
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Applying that to the previous example: |
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@example |
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ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg |
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@end example |
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Beware that there is no "jpeg" codec. Use "mjpeg" instead. |
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@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it? |
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No. FFmpeg only supports open source codecs. Windows DLLs are not |
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portable, bloated and often slow. |
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@section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem? |
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This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work. |
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@section Why do I see a slight quality degradation with multithreaded MPEG* encoding? |
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For multithreaded MPEG* encoding, the encoded slices must be independent, |
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otherwise thread n would practically have to wait for n-1 to finish, so it's |
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quite logical that there is a small reduction of quality. This is not a bug. |
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@section How can I read from the standard input or write to the standard output? |
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Use @file{-} as filename. |
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@section Why does ffmpeg not decode audio in VOB files? |
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The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg |
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as the component that handles AC3 decoding (liba52) is currently released under |
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the GPL. If you have liba52 installed on your system, enable AC3 decoding |
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with @code{./configure --enable-liba52 --enable-gpl}. Take care: by |
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enabling AC3, you automatically change the license of libavcodec from |
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LGPL to GPL. |
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@section Which codecs are supported by Windows? |
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Windows does not support standard formats like MPEG very well, unless you |
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install some additional codecs |
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The following list of video codecs should work on most Windows systems: |
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@table @option |
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@item msmpeg4v2 |
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.avi/.asf |
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@item msmpeg4 |
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.asf only |
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@item wmv1 |
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.asf only |
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@item wmv2 |
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.asf only |
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@item mpeg4 |
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only if you have some MPEG-4 codec installed like ffdshow or XviD |
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@item mpeg1 |
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.mpg only |
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@end table |
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Note, ASF files often have .wmv or .wma extensions in Windows. It should also |
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be mentioned that Microsoft claims a patent on the ASF format, and may sue |
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or threaten users who create ASF files with non-Microsoft software. It is |
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strongly advised to avoid ASF where possible. |
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The following list of audio codecs should work on most Windows systems: |
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@table @option |
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@item adpcm_ima_wav |
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@item adpcm_ms |
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@item pcm |
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@item mp3 |
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if some MP3 codec like LAME is installed |
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@end table |
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@section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux? |
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This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at |
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(@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-420-2.4.26.patch?view=co}). This may also |
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apply cleanly to other 2.4-series kernels. |
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@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux? |
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Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1' |
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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}) |
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or (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co}) |
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and pass 'combfilter=2'. |
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@section I have a problem with an old version of ffmpeg; where should I report it? |
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Nowhere. Upgrade to the latest release or if there is no recent release upgrade |
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to Subversion HEAD. You could also try to report it. Maybe you will get lucky and |
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become the first person in history to get an answer different from "upgrade |
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to Subversion HEAD". |
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@section -f jpeg doesn't work. |
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Try '-f image2 test%d.jpg'. |
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@section Why can I not change the framerate? |
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Some codecs, like MPEG-1/2, only allow a small number of fixed framerates. |
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Choose a different codec with the -vcodec command line option. |
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@section ffmpeg does not work; What is wrong? |
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Try a 'make distclean' in the ffmpeg source directory before the build. If this does not help see |
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(@url{http://ffmpeg.org/bugreports.php}). |
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@section How do I encode XviD or DivX video with ffmpeg? |
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Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4 |
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standard (note that there are many other coding formats that use this |
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same standard). Thus, use '-vcodec mpeg4' to encode these formats. The |
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default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want |
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a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will |
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force the fourcc 'xvid' to be stored as the video fourcc rather than the |
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default. |
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@section How do I encode videos which play on the iPod? |
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@table @option |
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@item needed stuff |
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-acodec libfaac -vcodec mpeg4 width<=320 height<=240 |
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@item working stuff |
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4mv, title |
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@item non-working stuff |
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B-frames |
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@item example command line |
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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 |
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@end table |
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@section How do I encode videos which play on the PSP? |
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@table @option |
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@item needed stuff |
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-acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp |
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@item working stuff |
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4mv, title |
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@item non-working stuff |
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B-frames |
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@item example command line |
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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 |
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@item needed stuff for H.264 |
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-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 |
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@item working stuff for H.264 |
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title, loop filter |
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@item non-working stuff for H.264 |
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CAVLC |
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@item example command line |
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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 |
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@end table |
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@section Which are good parameters for encoding high quality MPEG-4? |
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'-mbd rd -flags +4mv+trell+aic -cmp 2 -subcmp 2 -g 300 -pass 1/2', |
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things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'. |
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@section Which are good parameters for encoding high quality MPEG-1/MPEG-2? |
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'-mbd rd -flags +trell -cmp 2 -subcmp 2 -g 100 -pass 1/2' |
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but beware the '-g 100' might cause problems with some decoders. |
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Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd. |
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@section Interlaced video looks very bad when encoded with ffmpeg, whats wrong? |
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You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced |
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material, and try '-top 0/1' if the result looks really messed-up. |
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@section How can I read DirectShow files? |
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If you have built FFmpeg with @code{./configure --enable-avisynth} |
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(only possible on MinGW/Cygwin platforms), |
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then you may use any file that DirectShow can read as input. |
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(Be aware that this feature has been recently added, |
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so you will need to help yourself in case of problems.) |
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Just create an "input.avs" text file with this single line ... |
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@example |
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DirectShowSource("C:\path to your file\yourfile.asf") |
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@end example |
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... and then feed that text file to FFmpeg: |
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@example |
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ffmpeg -i input.avs |
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@end example |
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For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}. |
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@section My bugreport/mail to ffmpeg-devel/user has not received any replies. |
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Likely reasons |
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@itemize |
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@item We are busy and haven't had time yet to read your report or |
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investigate the issue. |
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@item You didn't follow bugreports.html. |
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@item You didn't use Subversion HEAD. |
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@item You reported a segmentation fault without gdb output. |
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@item You describe a problem but not how to reproduce it. |
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@item It's unclear if you use ffmpeg as command line tool or use |
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libav* from another application. |
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@item You speak about a video having problems on playback but |
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not what you use to play it. |
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@item We have no faint clue what you are talking about besides |
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that it is related to FFmpeg. |
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@end itemize |
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@section How can I join video files? |
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A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by |
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merely concatenating them. |
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Hence you may concatenate your multimedia files by first transcoding them to |
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these privileged formats, then using the humble @code{cat} command (or the |
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equally humble @code{copy} under Windows), and finally transcoding back to your |
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format of choice. |
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@example |
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ffmpeg -i input1.avi -sameq intermediate1.mpg |
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ffmpeg -i input2.avi -sameq intermediate2.mpg |
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cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg |
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ffmpeg -i intermediate_all.mpg -sameq output.avi |
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@end example |
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Notice that you should either use @code{-sameq} or set a reasonably high |
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bitrate for your intermediate and output files, if you want to preserve |
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video quality. |
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Also notice that you may avoid the huge intermediate files by taking advantage |
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of named pipes, should your platform support it: |
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@example |
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mkfifo intermediate1.mpg |
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mkfifo intermediate2.mpg |
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ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null & |
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ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null & |
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cat intermediate1.mpg intermediate2.mpg |\ |
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ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi |
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@end example |
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Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also |
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allow concatenation, and the transcoding step is almost lossless. |
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For example, let's say we want to join two FLV files into an output.flv file: |
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@example |
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mkfifo temp1.a |
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mkfifo temp1.v |
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mkfifo temp2.a |
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mkfifo temp2.v |
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mkfifo all.a |
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mkfifo all.v |
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ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null & |
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ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null & |
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ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null & |
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ffmpeg -i input2.flv -an -f yuv4mpegpipe - > temp2.v < /dev/null & |
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cat temp1.a temp2.a > all.a & |
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cat temp1.v temp2.v > all.v & |
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ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \ |
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-f yuv4mpegpipe -i all.v \ |
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-sameq -y output.flv |
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rm temp[12].[av] all.[av] |
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@end example |
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@section Is there a forum for FFmpeg, I do not like mailing lists? |
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Yes, (@url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user}). |
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@section FFmpeg does not adhere to the -maxrate setting, some frames are bigger than maxrate/fps. |
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Read the MPEG spec about video buffer verifier. |
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@section I want CBR, but no matter what I do frame sizes differ. |
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You do not understand what CBR is, please read the MPEG spec. |
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Read about video buffer verifier and constant bitrate. |
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The one sentence summary is that there is a buffer and the input rate is |
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constant, the output can vary as needed. |
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@section How do I check if a stream is CBR? |
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To quote the MPEG-2 spec: |
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"There is no way to tell that a bitstream is constant bitrate without |
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examining all of the vbv_delay values and making complicated computations." |
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@chapter Development |
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@section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between? |
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Like most open source projects FFmpeg suffers from a certain lack of |
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manpower. For this reason the developers have to prioritize the work |
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they do and putting out releases is not at the top of the list, fixing |
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bugs and reviewing patches takes precedence. Please don't complain or |
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request more timely and/or frequent releases unless you are willing to |
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help out creating them. |
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@section Why doesn't FFmpeg support feature [xyz]? |
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Because no one has taken on that task yet. FFmpeg development is |
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driven by the tasks that are important to the individual developers. |
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If there is a feature that is important to you, the best way to get |
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it implemented is to undertake the task yourself. |
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@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat? |
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Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively, |
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examine the source code for one of the many open source projects that |
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already incorporate ffmpeg at (@url{projects.php}). |
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@section Can you support my C compiler XXX? |
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It depends. If your compiler is C99-compliant, then patches to support |
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it are likely to be welcome if they do not pollute the source code |
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with @code{#ifdef}s related to the compiler. |
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@section Visual C++ produces many errors. |
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Visual C++ is not compliant to the C standard and does not support |
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the inline assembly used in FFmpeg. |
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If you wish - for whatever weird reason - to use Visual C++ for your |
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project then you can link the Visual C++ code with libav* as long as |
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you compile the latter with a working C compiler. For more information, see |
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the @emph{Visual C++ compatibility} section in the FFmpeg documentation. |
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There have been efforts to make FFmpeg compatible with Visual C++ in the |
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past. However, they have all been rejected as too intrusive, especially |
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since MinGW does the job perfectly adequately. None of the core developers |
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work with Visual C++ and thus this item is low priority. Should you find |
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the silver bullet that solves this problem, feel free to shoot it at us. |
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@section Can I use FFmpeg or libavcodec under Windows? |
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Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You |
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can link the resulting DLLs with any other Windows program. Read the |
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@emph{Native Windows Compilation} and @emph{Visual C++ compatibility} |
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sections in the FFmpeg documentation to find more information. |
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To get help and instructions for using FFmpeg under Windows, check out |
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the FFmpeg Windows Help Forum at |
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@url{http://arrozcru.no-ip.org/ffmpeg/}. |
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@section Can you add automake, libtool or autoconf support? |
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No. These tools are too bloated and they complicate the build. |
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@section Why not rewrite ffmpeg in object-oriented C++? |
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ffmpeg is already organized in a highly modular manner and does not need to |
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be rewritten in a formal object language. Further, many of the developers |
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favor straight C; it works for them. For more arguments on this matter, |
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read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}). |
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@section Why are the ffmpeg programs devoid of debugging symbols? |
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The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug |
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information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If |
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you need the debug information, used the *_g versions. |
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@section I do not like the LGPL, can I contribute code under the GPL instead? |
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Yes, as long as the code is optional and can easily and cleanly be placed |
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under #ifdef CONFIG_GPL without breaking anything. So for example a new codec |
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or filter would be OK under GPL while a bugfix to LGPL code would not. |
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@section I want to compile xyz.c alone but my compiler produced many errors. |
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Common code is in its own files in libav* and is used by the individual |
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codecs. They will not work without the common parts, you have to compile |
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the whole libav*. If you wish, disable some parts with configure switches. |
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You can also try to hack it and remove more, but if you had problems fixing |
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the compilation failure then you are probably not qualified for this. |
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@section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available. |
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FFmpeg is a pure C project, so to use the libraries within your C++ application |
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you need to explicitly state that you are using a C library. You can do this by |
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encompassing your FFmpeg includes using @code{extern "C"}. |
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See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3} |
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@section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat? |
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You have to implement a URLProtocol, see libavformat/file.c in FFmpeg |
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and libmpdemux/demux_lavf.c in MPlayer sources. |
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@section I get "No compatible shell script interpreter found." in MSys. |
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The standard MSys bash (2.04) is broken. You need to install 2.05 or later. |
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@section I tried to pass RTP packets into a decoder, but it doesn't work. |
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RTP is a container format like any other, you must first depacketize the |
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codec frames/samples stored in RTP and then feed to the decoder. |
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@section Where can I find libav* headers for Pascal/Delphi? |
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see @url{http://www.iversenit.dk/dev/ffmpeg-headers/} |
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@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm? |
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see @url{http://svn.mplayerhq.hu/michael/trunk/docs/} |
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@section how do I feed H.263-RTP (and other codecs in RTP) to libavcodec? |
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Even if peculiar since it is network oriented, RTP is a container like any |
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other. You have to @emph{demux} RTP before feeding the payload to libavcodec. |
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In this specific case please look at RFC 4629 to see how it should be done. |
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@section AVStream.r_frame_rate is wrong, its much larger than the frame rate |
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r_frame_rate is NOT the average framerate, it is the smallest framerate |
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with which all timestamps can be accurately represented, so no it is not |
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wrong if its larger than the average! |
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for example if you have 25 and 30 fps content mixed then r_frame_rate |
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will be 150. |
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@bye
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