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\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 Questions
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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 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 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 or sponsor a developer.
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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. Windows DLLs are not portable, bloated and often slow.
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Moreover FFmpeg strives to support all codecs natively.
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A DLL loader is not conducive to that goal.
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@section My bug report/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 Is there a forum for FFmpeg? I do not like mailing lists.
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You may view our mailing lists with a more forum-alike look here:
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@url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user},
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but, if you post, please remember that our mailing list rules still apply there.
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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 container 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 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 like ffdshow or Xvid installed.
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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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always
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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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@chapter Compilation
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@section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}
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This is a bug in gcc. Do not report it to us. Instead, please report it to
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the gcc developers. Note that we will not add workarounds for gcc bugs.
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Also note that (some of) the gcc developers believe this is not a bug or
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not a bug they should fix:
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@url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}.
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Then again, some of them do not know the difference between an undecidable
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problem and an NP-hard problem...
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@chapter Usage
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@section ffmpeg does not work; what is wrong?
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Try a @code{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.html}).
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@section How do I encode single pictures into movies?
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129 1fee8b3a Víctor Paesa
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 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 file name.
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@section Why does FFmpeg not decode audio in VOB files?
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The audio is AC-3 (a.k.a. A/52). AC-3 decoding is an optional component in FFmpeg
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as the component that handles AC-3 decoding is currently released under the GPL.
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Enable AC-3 decoding with @code{./configure --enable-gpl}. Take care: By
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enabling AC-3, you automatically change the license of libavcodec from
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LGPL to GPL.
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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.ffmpeg.org/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.ffmpeg.org/michael/trunk/patches/bttv-comb-2.4.26.patch?view=co})
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or (@url{http://svn.ffmpeg.org/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co})
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and pass 'combfilter=2'.
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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 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 in 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 -trellis 2 -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 -trellis 2 -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 libx264 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 libx264 -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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@item higher resolution for newer PSP firmwares, width<=480, height<=272
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-vcodec libx264 -level 21 -coder 1 -f psp
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@item example command line
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ffmpeg -i input -acodec libfaac -ab 128kb -ac 2 -ar 48000 -vcodec libx264 -level 21 -b 640kb -coder 1 -f psp -flags +loop -trellis 2 -partitions +parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 -g 250 -s 480x272 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+aic -trellis 2 -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 -trellis 2 -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, what is wrong?
269 c62997a5 Michael Niedermayer
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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 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 FFmpeg does not adhere to the -maxrate setting, some frames are bigger than maxrate/fps.
350 3b36389a Michael Niedermayer
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Read the MPEG spec about video buffer verifier.
352 3b36389a Michael Niedermayer
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@section I want CBR, but no matter what I do frame sizes differ.
354 3b36389a Michael Niedermayer
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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 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.html}).
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@section Can you support my C compiler XXX?
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377 e867d9b9 Diego Biurrun
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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381 a9d5a448 Diego Biurrun
@section Is Microsoft Visual C++ supported?
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383 a9d5a448 Diego Biurrun
No. Microsoft Visual C++ is not compliant to the C99 standard and does
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not - among other things - support the inline assembly used in FFmpeg.
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If you wish to use MSVC++ for your
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project then you can link the MSVC++ 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{Microsoft Visual C++ compatibility} section in the FFmpeg
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documentation.
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391 c1989552 Ramiro Polla
There have been efforts to make FFmpeg compatible with MSVC++ 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 adequately. None of the core developers
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work with MSVC++ 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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We strongly recommend you to move over from MSVC++ to MinGW tools.
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@section Can I use FFmpeg or libavcodec under Windows?
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401 c1989552 Ramiro Polla
Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg.
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Read the @emph{Windows} section in the FFmpeg documentation to find more
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information.
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To get help and instructions for building FFmpeg under Windows, check out
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the FFmpeg Windows Help Forum at
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@url{http://ffmpeg.arrozcru.org/}.
408 e2ef53fc Diego Biurrun
409 5965e1a9 Víctor Paesa
@section Can you add automake, libtool or autoconf support?
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411 e867d9b9 Diego Biurrun
No. These tools are too bloated and they complicate the build.
412 7ff56c72 Fabrice Bellard
413 5965e1a9 Víctor Paesa
@section Why not rewrite ffmpeg in object-oriented C++?
414 fbf33e4f Michael Niedermayer
415 831ec935 Diego Biurrun
FFmpeg is already organized in a highly modular manner and does not need to
416 115329f1 Diego Biurrun
be rewritten in a formal object language. Further, many of the developers
417 cacf7199 Mike Melanson
favor straight C; it works for them. For more arguments on this matter,
418 bc155732 Diego Biurrun
read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
419 cacf7199 Mike Melanson
420 5965e1a9 Víctor Paesa
@section Why are the ffmpeg programs devoid of debugging symbols?
421 cacf7199 Mike Melanson
422
The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
423 831ec935 Diego Biurrun
information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
424 cacf7199 Mike Melanson
you need the debug information, used the *_g versions.
425 fbf33e4f Michael Niedermayer
426 5965e1a9 Víctor Paesa
@section I do not like the LGPL, can I contribute code under the GPL instead?
427 61a1e081 Michael Niedermayer
428 e180129f Diego Biurrun
Yes, as long as the code is optional and can easily and cleanly be placed
429 b250f9c6 Aurelien Jacobs
under #if CONFIG_GPL without breaking anything. So for example a new codec
430 831ec935 Diego Biurrun
or filter would be OK under GPL while a bug fix to LGPL code would not.
431 61a1e081 Michael Niedermayer
432 e180129f Diego Biurrun
@section I want to compile xyz.c alone but my compiler produced many errors.
433 61a1e081 Michael Niedermayer
434 e180129f Diego Biurrun
Common code is in its own files in libav* and is used by the individual
435
codecs. They will not work without the common parts, you have to compile
436
the whole libav*. If you wish, disable some parts with configure switches.
437
You can also try to hack it and remove more, but if you had problems fixing
438
the compilation failure then you are probably not qualified for this.
439 61a1e081 Michael Niedermayer
440 4cb3aa09 Panagiotis Issaris
@section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available.
441
442
FFmpeg is a pure C project, so to use the libraries within your C++ application
443
you need to explicitly state that you are using a C library. You can do this by
444
encompassing your FFmpeg includes using @code{extern "C"}.
445
446
See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
447
448 2cab6401 Diego Biurrun
@section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
449 f994f61e Michael Niedermayer
450 1c1b5a40 Diego Biurrun
You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
451
and libmpdemux/demux_lavf.c in MPlayer sources.
452 f994f61e Michael Niedermayer
453 e9766450 Ramiro Polla
@section I get "No compatible shell script interpreter found." in MSys.
454
455
The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
456
457 e75f8997 Ramiro Polla
@section I get "./configure: line <xxx>: pr: command not found" in MSys.
458
459
The standard MSys install doesn't come with pr. You need to get it from the coreutils package.
460
461 5c159f40 Diego Biurrun
@section I tried to pass RTP packets into a decoder, but it doesn't work.
462 b72ad042 Michael Niedermayer
463 241fb0c4 Luca Barbato
RTP is a container format like any other, you must first depacketize the
464
codec frames/samples stored in RTP and then feed to the decoder.
465 b72ad042 Michael Niedermayer
466 7c1ebf17 Diego Biurrun
@section Where can I find libav* headers for Pascal/Delphi?
467 04704a78 Michael Niedermayer
468
see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
469
470 7c1ebf17 Diego Biurrun
@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
471 afe28f7c Michael Niedermayer
472 0fa5f24c Diego Biurrun
see @url{http://svn.ffmpeg.org/michael/trunk/docs/}
473 afe28f7c Michael Niedermayer
474 29569571 Diego Biurrun
@section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
475 8749180c Michael Niedermayer
476 241fb0c4 Luca Barbato
Even if peculiar since it is network oriented, RTP is a container like any
477 33ed2d84 Luca Barbato
other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
478
In this specific case please look at RFC 4629 to see how it should be done.
479 8749180c Michael Niedermayer
480 29569571 Diego Biurrun
@section AVStream.r_frame_rate is wrong, it is much larger than the framerate.
481 70fd3975 Michael Niedermayer
482
r_frame_rate is NOT the average framerate, it is the smallest framerate
483 29569571 Diego Biurrun
that can accurately represent all timestamps. So no, it is not
484
wrong if it is larger than the average!
485
For example, if you have mixed 25 and 30 fps content, then r_frame_rate
486 70fd3975 Michael Niedermayer
will be 150.
487
488 7ff56c72 Fabrice Bellard
@bye