\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 I cannot read this file although this format seems to be supported by ffmpeg.
+@chapter General Questions
-Even if ffmpeg can read the file format, it may not support all its
-codecs. Please consult the supported codec list in the ffmpeg
-documentation.
-
-@section How do I encode JPEGs to another format ?
-
-If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:
-
-@example
- ffmpeg -f image2 -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 How do I encode movie to single pictures ?
-
-Use:
-
-@example
- ffmpeg -i movie.mpg movie%d.jpg
-@end example
-
-The @file{movie.mpg} used as input will be converted to
-@file{movie1.jpg}, @file{movie2.jpg}, etc...
-
-Instead of relying on file format self-recognition, you may also use
-@table @option
-@item -vcodec ppm
-@item -vcodec png
-@item -vcodec mjpeg
-@end table
-to force the encoding.
-
-Applying that to the previous example:
-@example
- ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
-@end example
-
-Beware that there is no "jpeg" codec. Use "mjpeg" instead.
-
-@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
-
-No. FFmpeg only supports open source codecs. Windows DLLs are not
-portable, bloated and often slow.
+@section Why doesn't Libav support feature [xyz]?
-@section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem ?
-
-This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work.
-
-@section Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
-
-For multithreaded MPEG* encoding, the encoded slices must be independent,
-otherwise thread n would practically have to wait for n-1 to finish, so it's
-quite logical that there is a small reduction of quality. This is not a bug.
+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.
-@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 does ffmpeg not decode audio in VOB files ?
+@section I cannot read this file although this format seems to be supported by avconv.
-The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
-as the component that handles AC3 decoding (liba52) is currently released under
-the GPL. If you have liba52 installed on your system, enable AC3 decoding
-with @code{./configure --enable-liba52 --enable-gpl}. Take care: by
-enabling AC3, you automatically change the license of libavcodec from
-LGPL to GPL.
+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
+install some additional codecs.
The following list of video codecs should work on most Windows systems:
@table @option
@item wmv2
.asf only
@item mpeg4
-only if you have some MPEG-4 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 files often have .wmv or .wma extensions in Windows. It should also
@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
+
+
+@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.
-@section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
+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.
-This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
-(@url{http://mplayerhq.hu/~michael/bttv-420-2.4.26.patch}). This may also
-apply cleanly to other 2.4-series kernels.
+@section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
-@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
+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.
-Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
-will cause somewhat too strong filtering. A fix is to apply (@url{http://mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
-or (@url{http://mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
-and pass 'combfilter=2'.
+@section How can I read from the standard input or write to the standard output?
-@section I have a problem with an old version of ffmpeg; where should I report it?
-Nowhere. Upgrade to the latest release or if there is no recent release upgrade
-to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
-become the first person in history to get an answer different from "upgrade
-to Subversion HEAD".
+Use @file{-} as file name.
@section -f jpeg doesn't work.
@section Why can I not change the framerate?
Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
-Choose a different codec with the -vcodec command line option.
+Choose a different codec with the -c:v command line option.
-@section ffmpeg does not work; What is wrong?
+@section How do I encode Xvid or DivX video with avconv?
-Try a 'make distclean' in the ffmpeg source directory before the build. If this does not help see
-(@url{http://ffmpeg.org/bugreports.php}).
-
-@section How do I encode XviD or DivX video with ffmpeg?
-
-Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
+Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
standard (note that there are many other coding formats that use this
-same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
+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 How do I encode videos which play on the iPod?
-
-@table @option
-@item needed stuff
--acodec aac -vcodec mpeg4 width<=320 height<=240
-@item working stuff
-4mv, title
-@item non-working stuff
-B-frames
-@item example command line
-ffmpeg -i input -acodec aac -ab 128kb -vcodec mpeg4 -b 1200kb -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 320x180 -title X output.mp4
-@end table
-
-@section How do I encode videos which play on the PSP?
-
-@table @option
-@item needed stuff
--acodec aac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
-@item working stuff
-4mv, title
-@item non-working stuff
-B-frames
-@item example command line
-ffmpeg -i input -acodec aac -ab 128kb -vcodec mpeg4 -b 1200kb -ar 24000 -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp output.mp4
-@item needed stuff for H.264
--acodec aac -vcodec h264 width*height<=76800 width%16=0? height%16=0? -ar 48000 -coder 1 -r 30000/1001 or 15000/1001 -f psp
-@item working stuff for H.264
-title, loop filter
-@item non-working stuff for H.264
-CAVLC
-@item example command line
-ffmpeg -i input -acodec aac -ab 128kb -vcodec h264 -b 1200kb -ar 48000 -mbd 2 -coder 1 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp -flags loop -trellis 2 -partitions parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 output.mp4
-@end table
-
@section Which are good parameters for encoding high quality MPEG-4?
-'-mbd rd -flags +4mv+trell+aic -cmp 2 -subcmp 2 -g 300 -pass 1/2',
+'-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 -flags +trell -cmp 2 -subcmp 2 -g 100 -pass 1/2'
+'-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 ffmpeg, whats wrong?
+@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 FFmpeg with @code{./configure --enable-avisynth}
+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.
-(Be aware that this feature has been recently added,
-so you will need to help yourself in case of problems.)
Just create an "input.avs" text file with this single line ...
@example
DirectShowSource("C:\path to your file\yourfile.asf")
@end example
-... and then feed that text file to FFmpeg:
+... and then feed that text file to avconv:
@example
- ffmpeg -i input.avs
+ avconv -i input.avs
@end example
-For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
-
-@section My bugreport/mail to ffmpeg-devel/user has not received any replies.
-
-Likely reasons
-@itemize
-@item We are busy and haven't had time yet to read your report or
-investigate the issue.
-@item You didn't follow bugreports.html.
-@item You didn't use Subversion HEAD.
-@item You reported a segmentation fault without gdb output.
-@item You describe a problem but not how to reproduce it.
-@item It's unclear if you use ffmpeg as command line tool or use
-libav* from another application.
-@item You speak about a video having problems on playback but
-not what you use to play it.
-@item We have no faint clue what you are talking about besides
-that it is related to FFmpeg.
-@end itemize
+For ANY other help on Avisynth, please visit the
+@uref{http://www.avisynth.org/, Avisynth homepage}.
-@chapter Development
+@section How can I join video files?
-@section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
+A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
+merely concatenating them.
-Like most open source projects FFmpeg suffers from a certain lack of
-manpower. For this reason the developers have to prioritize the work
-they do and putting out releases is not at the top of the list, fixing
-bugs and reviewing patches takes precedence. Please don't complain or
-request more timely and/or frequent releases unless you are willing to
-help out creating 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.
-@section Why doesn't FFmpeg support feature [xyz]?
+@example
+avconv -i input1.avi -same_quant intermediate1.mpg
+avconv -i input2.avi -same_quant intermediate2.mpg
+cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
+avconv -i intermediate_all.mpg -same_quant output.avi
+@end example
-Because no one has taken on that task yet. FFmpeg 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.
+Notice that you should either use @code{-same_quant} or 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 -same_quant -y intermediate1.mpg < /dev/null &
+avconv -i input2.avi -same_quant -y intermediate2.mpg < /dev/null &
+cat intermediate1.mpg intermediate2.mpg |\
+avconv -f mpeg -i - -same_quant -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 \
+ -same_quant -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}.
-@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
+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.
-Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
+@chapter Development
+
+@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 ffmpeg at (@url{projects.php}).
+already incorporate Libav at (@url{projects.html}).
-@section Can you support my C compiler XXX ?
+@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 Visual C++ produces many errors.
+@section Is Microsoft Visual C++ supported?
-Visual C++ is not compliant to the C standard and does not support
-the inline assembly used in FFmpeg.
-If you wish - for whatever weird reason - to use Visual C++ for your
-project then you can link the Visual C++ code with libav* as long as
+No. Microsoft Visual C++ is not compliant to the C99 standard and does
+not - among other things - support the inline assembly used in Libav.
+If you wish to use MSVC++ for your
+project then you can link the MSVC++ code with libav* as long as
you compile the latter with a working C compiler. For more information, see
-the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
+the @emph{Microsoft Visual C++ compatibility} section in the Libav
+documentation.
-There have been efforts to make FFmpeg compatible with Visual C++ in the
+There have been efforts to make Libav compatible with MSVC++ in the
past. However, they have all been rejected as too intrusive, especially
-since MinGW does the job perfectly adequately. None of the core developers
-work with Visual C++ and thus this item is low priority. Should you find
+since MinGW does the job adequately. None of the core developers
+work with MSVC++ and thus this item is low priority. Should you find
the silver bullet that solves this problem, feel free to shoot it at us.
-@section Can I use FFmpeg or libavcodec under Windows ?
+We strongly recommend you to move over from MSVC++ to MinGW tools.
-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} and @emph{Visual C++ compatibility}
-sections in the FFmpeg documentation to find more information.
+@section Can I use Libav under Windows?
-To get help and instructions for using FFmpeg under Windows, check out
-the FFmpeg Windows Help Forum at
-@url{http://arrozcru.no-ip.org/ffmpeg/}.
+Yes, but the Cygwin or MinGW tools @emph{must} be used to compile Libav.
+Read the @emph{Windows} section in the Libav documentation to find more
+information.
-@section Can you add automake, libtool or autoconf support ?
+@section Can you add automake, libtool or autoconf support?
No. These tools are too bloated and they complicate the build.
-@section Why not rewrite ffmpeg in object-oriented C++ ?
+@section Why not rewrite Libav in object-oriented C++?
-ffmpeg is already organized in a highly modular manner and does not need to
+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 "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
+read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
-@section Why are the ffmpeg programs devoid of debugging symbols ?
-
-The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
-information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
-you need the debug information, used the *_g versions.
-
-@section I do not like the LGPL, can I contribute code under the GPL instead ?
+@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 #ifdef CONFIG_GPL without breaking anything. So for example a new codec
-or filter would be OK under GPL while a bugfix to LGPL code would not.
-
-@section I want to compile xyz.c alone but my compiler produced many errors.
+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.
-Common code is in its own files in libav* and is used by the individual
-codecs. They will not work without the common parts, you have to compile
-the whole libav*. If you wish, disable some parts with configure switches.
-You can also try to hack it and remove more, but if you had problems fixing
-the compilation failure then you are probably not qualified for this.
+@section I'm using Libav from within my C++ application but the linker complains about missing symbols which seem to be available.
-@section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat ?
+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"}.
-You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
-and libmpdemux/demux_lavf.c in MPlayer sources.
+See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
-@section I get "No compatible shell script interpreter found." in MSys.
+@section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope
-The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
+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 I tried to pass RTP packets into a decoder, but it doesn't work.
+@section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
-Of course not, you MUST strip ALL RTP headers and assemble valid packets
-first, an MP3 decoder decodes MP3 packets not bastardized MP3 packets
-encapsulated in RTP. The same applies to all decoders, this is not specific
-to ffmpeg or libavcodec.
+You have to implement a URLProtocol, see @file{libavformat/file.c} in
+Libav and @file{libmpdemux/demux_lavf.c} in MPlayer sources.
-@section where can i find libav* headers for pascal/delphi
+@section Why is @code{make fate} not running all tests?
-see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
+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 where are docs about ffv1, msmpeg4, asv1, 4xm?
+@section Why is @code{make fate} not finding the samples?
-see @url{http://svn.mplayerhq.hu/michael/trunk/docs/}
+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