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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 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 I get audio/video synchronization problems when grabbing.
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Currently, the grabbing stuff does not handle synchronisation
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correctly. You are free to correct it. A fix is planned.
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@section How do I encode JPEGs to another format ?
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If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:
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@example
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  ffmpeg -i img%d.jpg /tmp/a.mpg
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@end example
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@samp{%d} is replaced by the image number.
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@file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...
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The same system is used for the other image formats.
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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 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-a52}. 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://mplayerhq.hu/~michael/bttv-420-2.4.26.patch}). 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://mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
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or (@url{http://mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
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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 CVS. 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 CVS".
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@section -f jpeg doesn't work.
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Try '-f image -img jpeg 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. 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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@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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No. Only GCC is supported. GCC is ported to most systems available and there
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is no need to pollute the source code with @code{#ifdef}s
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related to the compiler.
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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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@section Can you add automake, libtool or autoconf support ?
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No. These tools are too bloated and they complicate the build. Moreover,
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since only @samp{gcc} is supported they would add little advantages in
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terms of portability.
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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://lkml.org/faq/lkmlfaq-15.html}).
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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 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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@bye