\input texinfo @c -*- texinfo -*-
-@settitle FFmpeg FAQ
+@settitle Libav FAQ
@titlepage
-@sp 7
-@center @titlefont{FFmpeg FAQ}
-@sp 3
+@center @titlefont{Libav FAQ}
@end titlepage
+@top
-@chapter General Problems
+@contents
-@section ffserver doesn't not work.
+@chapter General Questions
-ffmpeg development is now concentrated on the codec and format
-handling. New developments broke ffserver, so don't expect it to work
-correctly. It is planned to fix it ASAP.
+@section Why doesn't Libav support feature [xyz]?
-@section I cannot read this file although this format seems to be suppored by ffmpeg.
+Because no one has taken on that task yet. Libav development is
+driven by the tasks that are important to the individual developers.
+If there is a feature that is important to you, the best way to get
+it implemented is to undertake the task yourself or sponsor a developer.
-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 I get audio/video synchro problems when grabbing.
-
-Currently, the grabbing stuff does not handle synchronisation
-correctly. You are free to correct it. It is planned to fix it ASAP.
-
-@section How do I encode jpegs to another format ?
-
-If the jpegs are named img1.jpg, img2.jpg, img3.jpg,..., use:
-
-@example
- ffmpeg -i img%d.jpg /tmp/a.mpg
-@end example
-
-@samp{%d} is replaced by the image number.
-
-@file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...
-
-The same system is used for the other image formats.
-
-@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 How can I read from the standard input or write to the standard output ?
+@section Libav does not support codec XXX. Can you include a Windows DLL loader to support it?
-Use @file{-} as filename.
+No. Windows DLLs are not portable, bloated and often slow.
+Moreover Libav strives to support all codecs natively.
+A DLL loader is not conducive to that goal.
-@section Why Audio is not decoded in VOB files ?
+@section I cannot read this file although this format seems to be supported by avconv.
-AC3 decoding is optional as the codec is currently released under the
-GPL. Enable it with @code{./configure --enable-a52}. Take care: by
-enabling AC3, you automatically change the license of libavcodec from
-LGPL to GPL.
+Even if avconv can read the container format, it may not support all its
+codecs. Please consult the supported codec list in the avconv
+documentation.
-@section Which codecs are supported by windows ?
+@section Which codecs are supported by Windows?
-Windows does not support standard formats like mpeg very well, unless you
-install some additional codecs
+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
+The following list of video codecs should work on most Windows systems:
@table @option
@item msmpeg4v2
.avi/.asf
@item wmv2
.asf only
@item mpeg4
-only if you have some mpeg4 codec installed like ffdshow or xvid
-@item mpeg1
+Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
+@item mpeg1video
.mpg only
@end table
-note, asf often uses .wmv or .wma extensions in windows, it should also be
-mentioned that asf is patented, so microsoft may sue or threaten users who
-use it if they see any reason to do so, it is strongly recommanded to avoid asf
-for any use
+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
+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
+@item pcm_s16le
+always
+@item libmp3lame
+If some MP3 codec like LAME is installed.
@end table
-@section The chrominance seems to come from a different time then the luminance on bt8x8 captures on linux?
-well known bug in the bt8x8 driver, for 2.4.26 theres a patch at
-(@url{http://www.mplayerhq.hu/~michael/bttv-420-2.4.26.patch}), i suspect that
-this will also apply cleanly to other 2.4 kernels
+@chapter Compilation
+
+@section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}
+
+This is a bug in gcc. Do not report it to us. Instead, please report it to
+the gcc developers. Note that we will not add workarounds for gcc bugs.
+
+Also note that (some of) the gcc developers believe this is not a bug or
+not a bug they should fix:
+@url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}.
+Then again, some of them do not know the difference between an undecidable
+problem and an NP-hard problem...
+
+@chapter Usage
+
+@section How do I encode single pictures into movies?
+
+First, rename your pictures to follow a numerical sequence.
+For example, img1.jpg, img2.jpg, img3.jpg,...
+Then you may run:
+
+@example
+ avconv -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...
+
+If you have large number of pictures to rename, you can use the
+following command to ease the burden. The command, using the bourne
+shell syntax, symbolically links all files in the current directory
+that match @code{*jpg} to the @file{/tmp} directory in the sequence of
+@file{img001.jpg}, @file{img002.jpg} and so on.
+
+@example
+ x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
+@end example
+
+If you want to sequence them by oldest modified first, substitute
+@code{$(ls -r -t *jpg)} in place of @code{*jpg}.
+
+Then run:
+
+@example
+ avconv -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
+@end example
+
+The same logic is used for any image format that avconv reads.
+
+@section How do I encode movie to single pictures?
+
+Use:
+
+@example
+ avconv -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 -c:v ppm
+@item -c:v png
+@item -c:v mjpeg
+@end table
+to force the encoding.
+
+Applying that to the previous example:
+@example
+ avconv -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg
+@end example
+
+Beware that there is no "jpeg" codec. Use "mjpeg" instead.
+
+@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 file name.
-@section How to avoid the ugly aliassing artefacts in bt8x8 captures on linux?
+@section -f jpeg doesn't work.
-pass 'combfilter=1 lumafilter=1' to the bttv driver, note though that 'combfilter=1'
-will cause somewhat too strong filtering, a fix is too apply (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
-or (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
-and pass 'combfilter=2'
+Try '-f image2 test%d.jpg'.
-@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 cvs, you could also try to report it, maybe you are lucky and
-will become the first person in history to get a different awnser from "upgrade
-to cvs".
+@section Why can I not change the framerate?
-@section -f jpeg doesnt work.
+Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
+Choose a different codec with the -c:v command line option.
-try '-f image -img jpeg test%d.jpg'
+@section How do I encode Xvid or DivX video with avconv?
+
+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 '-c:v mpeg4' to encode in 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 Which are good parameters for encoding high quality MPEG-4?
+
+'-mbd rd -flags +mv4+aic -trellis 2 -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 -trellis 2 -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 avconv, what is 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 Libav with @code{./configure --enable-avisynth}
+(only possible on MinGW/Cygwin platforms),
+then you may use any file that DirectShow can read as input.
+
+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 avconv:
+@example
+ avconv -i input.avs
+@end example
+
+For ANY other help on AviSynth, please visit the
+@uref{http://www.avisynth.org/, AviSynth homepage}.
+
+@section How can I join video files?
+
+A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
+merely concatenating them.
+
+Hence you may concatenate your multimedia files by first transcoding them to
+these privileged formats, then using the humble @code{cat} command (or the
+equally humble @code{copy} under Windows), and finally transcoding back to your
+format of choice.
+
+@example
+avconv -i input1.avi intermediate1.mpg
+avconv -i input2.avi intermediate2.mpg
+cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
+avconv -i intermediate_all.mpg output.avi
+@end example
+
+Notice that you should set a reasonably high bitrate for your intermediate and
+output files, if you want to preserve video quality.
+
+Also notice that you may avoid the huge intermediate files by taking advantage
+of named pipes, should your platform support it:
+
+@example
+mkfifo intermediate1.mpg
+mkfifo intermediate2.mpg
+avconv -i input1.avi -y intermediate1.mpg < /dev/null &
+avconv -i input2.avi -y intermediate2.mpg < /dev/null &
+cat intermediate1.mpg intermediate2.mpg |\
+avconv -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi
+@end example
+
+Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
+allow concatenation, and the transcoding step is almost lossless.
+When using multiple yuv4mpegpipe(s), the first line needs to be discarded
+from all but the first stream. This can be accomplished by piping through
+@code{tail} as seen below. Note that when piping through @code{tail} you
+must use command grouping, @code{@{ ;@}}, to background properly.
+
+For example, let's say we want to join two FLV files into an output.flv file:
+
+@example
+mkfifo temp1.a
+mkfifo temp1.v
+mkfifo temp2.a
+mkfifo temp2.v
+mkfifo all.a
+mkfifo all.v
+avconv -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
+avconv -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
+avconv -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
+@{ avconv -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
+cat temp1.a temp2.a > all.a &
+cat temp1.v temp2.v > all.v &
+avconv -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
+ -f yuv4mpegpipe -i all.v \
+ -y output.flv
+rm temp[12].[av] all.[av]
+@end example
+
+@section -profile option fails when encoding H.264 video with AAC audio
+
+@command{avconv} prints an error like
+
+@example
+Undefined constant or missing '(' in 'baseline'
+Unable to parse option value "baseline"
+Error setting option profile to value baseline.
+@end example
+
+Short answer: write @option{-profile:v} instead of @option{-profile}.
+
+Long answer: this happens because the @option{-profile} option can apply to both
+video and audio. Specifically the AAC encoder also defines some profiles, none
+of which are named @var{baseline}.
+
+The solution is to apply the @option{-profile} option to the video stream only
+by using @url{http://libav.org/avconv.html#Stream-specifiers-1, Stream specifiers}.
+Appending @code{:v} to it will do exactly that.
@chapter Development
-@section Are there examples of use of the FFmpeg libraries libavcodec and libavformat ?
+@section Are there examples illustrating how to use the Libav libraries, particularly libavcodec and libavformat?
+
+Yes. Read the Developers Guide of the Libav documentation. Alternatively,
+examine the source code for one of the many open source projects that
+already incorporate Libav at (@url{projects.html}).
+
+@section Can you support my C compiler XXX?
+
+It depends. If your compiler is C99-compliant, then patches to support
+it are likely to be welcome if they do not pollute the source code
+with @code{#ifdef}s related to the compiler.
+
+@section Is Microsoft Visual C++ supported?
+
+Yes. Please see the @uref{platform.html, Microsoft Visual C++}
+section in the Libav documentation.
+
+@section Can you add automake, libtool or autoconf support?
+
+No. These tools are too bloated and they complicate the build.
+
+@section Why not rewrite Libav in object-oriented C++?
+
+Libav is already organized in a highly modular manner and does not need to
+be rewritten in a formal object language. Further, many of the developers
+favor straight C; it works for them. For more arguments on this matter,
+read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
+
+@section I do not like the LGPL, can I contribute code under the GPL instead?
+
+Yes, as long as the code is optional and can easily and cleanly be placed
+under #if CONFIG_GPL without breaking anything. So for example a new codec
+or filter would be OK under GPL while a bug fix to LGPL code would not.
+
+@section I'm using Libav from within my C++ application but the linker complains about missing symbols which seem to be available.
+
+Libav is a pure C project, so to use the libraries within your C++ application
+you need to explicitly state that you are using a C library. You can do this by
+encompassing your Libav includes using @code{extern "C"}.
-Yes. Read the Developers Guide of the FFmpeg documentation.
+See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
-@section Can you support my C compiler XXX ?
+@section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope
-No. Only GCC is supported. GCC is ported on most systems available and I
-don't see the need to pollute the source code with @code{#ifdef}s
-related to the compiler.
+Libav is a pure C project using C99 math features, in order to enable C++
+to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS
-@section Can I use FFmpeg or libavcodec under Windows ?
+@section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
-Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
-can link the resulting DLLs with any other Windows program. Read the
-@emph{Native Windows Compilation} section in the FFmpeg documentation
-to have more information.
+You have to create a custom AVIOContext using @code{avio_alloc_context},
+see @file{libavformat/aviobuf.c} in Libav and @file{libmpdemux/demux_lavf.c} in MPlayer2 sources.
-@section Can you add automake, libtool or autoconf support ?
+@section Why is @code{make fate} not running all tests?
-No. These tools are too blowted and they complicate the build. Moreover,
-since only @samp{gcc} is supported they would add little advantages in
-terms of portability.
+Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable
+or @code{FATE_SAMPLES} environment variable or the @code{--samples}
+@command{configure} option is set to the right path.
-@section ffmpeg doesnt contain any debugging symbols ?
+@section Why is @code{make fate} not finding the samples?
-try ffmpeg_g, ffplay_g, ...
+Do you happen to have a @code{~} character in the samples path to indicate a
+home directory? The value is used in ways where the shell cannot expand it,
+causing FATE to not find files. Just replace @code{~} by the full path.
@bye
projects / ffmpeg / blobdiff