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diff --git a/ffmpeg/doc/faq.texi b/ffmpeg/doc/faq.texi new file mode 100644 index 0000000..ebf21f5 --- /dev/null +++ b/ffmpeg/doc/faq.texi @@ -0,0 +1,558 @@ +\input texinfo @c -*- texinfo -*- + +@settitle FFmpeg FAQ +@titlepage +@center @titlefont{FFmpeg FAQ} +@end titlepage + +@top + +@contents + +@chapter General Questions + +@section Why doesn't FFmpeg support feature [xyz]? + +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 or sponsor a developer. + +@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it? + +No. Windows DLLs are not portable, bloated and often slow. +Moreover FFmpeg strives to support all codecs natively. +A DLL loader is not conducive to that goal. + +@section I cannot read this file although this format seems to be supported by ffmpeg. + +Even if ffmpeg can read the container format, it may not support all its +codecs. Please consult the supported codec list in the ffmpeg +documentation. + +@section Which codecs are supported by Windows? + +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: +@table @option +@item msmpeg4v2 +.avi/.asf +@item msmpeg4 +.asf only +@item wmv1 +.asf only +@item wmv2 +.asf only +@item mpeg4 +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 +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: +@table @option +@item adpcm_ima_wav +@item adpcm_ms +@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... + +@section I have installed this library with my distro's package manager. Why does @command{configure} not see it? + +Distributions usually split libraries in several packages. The main package +contains the files necessary to run programs using the library. The +development package contains the files necessary to build programs using the +library. Sometimes, docs and/or data are in a separate package too. + +To build FFmpeg, you need to install the development package. It is usually +called @file{libfoo-dev} or @file{libfoo-devel}. You can remove it after the +build is finished, but be sure to keep the main package. + +@chapter Usage + +@section ffmpeg does not work; what is wrong? + +Try a @code{make distclean} in the ffmpeg source directory before the build. +If this does not help see +(@url{http://ffmpeg.org/bugreports.html}). + +@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 + ffmpeg -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. + +Use the @option{-start_number} option to declare a starting number for +the sequence. This is useful if your sequence does not start with +@file{img001.jpg} but is still in a numerical order. The following +example will start with @file{img100.jpg}: + +@example + ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg +@end example + +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 + ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg +@end example + +The same logic is used for any image format that ffmpeg reads. + +You can also use @command{cat} to pipe images to ffmpeg: + +@example + cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg +@end example + +@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 -c:v ppm +@item -c:v png +@item -c:v mjpeg +@end table +to force the encoding. + +Applying that to the previous example: +@example + ffmpeg -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 -f jpeg doesn't work. + +Try '-f image2 test%d.jpg'. + +@section Why can I not change the frame rate? + +Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates. +Choose a different codec with the -c:v command line option. + +@section How do I encode Xvid or DivX video with ffmpeg? + +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 ffmpeg, 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} +(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 ffmpeg: +@example + ffmpeg -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? + +To "join" video files is quite ambiguous. The following list explains the +different kinds of "joining" and points out how those are addressed in +FFmpeg. To join video files may mean: + +@itemize + +@item +To put them one after the other: this is called to @emph{concatenate} them +(in short: concat) and is addressed +@ref{How can I concatenate video files, in this very faq}. + +@item +To put them together in the same file, to let the user choose between the +different versions (example: different audio languages): this is called to +@emph{multiplex} them together (in short: mux), and is done by simply +invoking ffmpeg with several @option{-i} options. + +@item +For audio, to put all channels together in a single stream (example: two +mono streams into one stereo stream): this is sometimes called to +@emph{merge} them, and can be done using the +@url{http://ffmpeg.org/ffmpeg-filters.html#amerge, @code{amerge}} filter. + +@item +For audio, to play one on top of the other: this is called to @emph{mix} +them, and can be done by first merging them into a single stream and then +using the @url{http://ffmpeg.org/ffmpeg-filters.html#pan, @code{pan}} filter to mix +the channels at will. + +@item +For video, to display both together, side by side or one on top of a part of +the other; it can be done using the +@url{http://ffmpeg.org/ffmpeg-filters.html#overlay, @code{overlay}} video filter. + +@end itemize + +@anchor{How can I concatenate video files} +@section How can I concatenate video files? + +There are several solutions, depending on the exact circumstances. + +@subsection Concatenating using the concat @emph{filter} + +FFmpeg has a @url{http://ffmpeg.org/ffmpeg-filters.html#concat, +@code{concat}} filter designed specifically for that, with examples in the +documentation. This operation is recommended if you need to re-encode. + +@subsection Concatenating using the concat @emph{demuxer} + +FFmpeg has a @url{http://www.ffmpeg.org/ffmpeg-formats.html#concat, +@code{concat}} demuxer which you can use when you want to avoid a re-encode and +your format doesn't support file level concatenation. + +@subsection Concatenating using the concat @emph{protocol} (file level) + +FFmpeg has a @url{http://ffmpeg.org/ffmpeg-protocols.html#concat, +@code{concat}} protocol designed specifically for that, with examples in the +documentation. + +A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenate +video by merely concatenating the files containing 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 +ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg +ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg +cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg +ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi +@end example + +Additionally, you can use the @code{concat} protocol instead of @code{cat} or +@code{copy} which will avoid creation of a potentially huge intermediate file. + +@example +ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg +ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg +ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg +ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi +@end example + +Note that you may need to escape the character "|" which is special for many +shells. + +Another option is usage of named pipes, should your platform support it: + +@example +mkfifo intermediate1.mpg +mkfifo intermediate2.mpg +ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null & +ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null & +cat intermediate1.mpg intermediate2.mpg |\ +ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi +@end example + +@subsection Concatenating using raw audio and video + +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 concatenate 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 +ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null & +ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null & +ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null & +@{ ffmpeg -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 & +ffmpeg -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{ffmpeg} 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://ffmpeg.org/ffmpeg.html#Stream-specifiers-1, Stream specifiers}. +Appending @code{:v} to it will do exactly that. + +@section Using @option{-f lavfi}, audio becomes mono for no apparent reason. + +Use @option{-dumpgraph -} to find out exactly where the channel layout is +lost. + +Most likely, it is through @code{auto-inserted aconvert}. Try to understand +why the converting filter was needed at that place. + +Just before the output is a likely place, as @option{-f lavfi} currently +only support packed S16. + +Then insert the correct @code{aconvert} explicitly in the filter graph, +specifying the exact format. + +@example +aconvert=s16:stereo:packed +@end example + +@section Why does FFmpeg not see the subtitles in my VOB file? + +VOB and a few other formats do not have a global header that describes +everything present in the file. Instead, applications are supposed to scan +the file to see what it contains. Since VOB files are frequently large, only +the beginning is scanned. If the subtitles happen only later in the file, +they will not be initally detected. + +Some applications, including the @code{ffmpeg} command-line tool, can only +work with streams that were detected during the initial scan; streams that +are detected later are ignored. + +The size of the initial scan is controlled by two options: @code{probesize} +(default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For +the subtitle stream to be detected, both values must be large enough. + +@section Why was the @command{ffmpeg} @option{-sameq} option removed? What to use instead? + +The @option{-sameq} option meant "same quantizer", and made sense only in a +very limited set of cases. Unfortunately, a lot of people mistook it for +"same quality" and used it in places where it did not make sense: it had +roughly the expected visible effect, but achieved it in a very inefficient +way. + +Each encoder has its own set of options to set the quality-vs-size balance, +use the options for the encoder you are using to set the quality level to a +point acceptable for your tastes. The most common options to do that are +@option{-qscale} and @option{-qmax}, but you should peruse the documentation +of the encoder you chose. + +@chapter Development + +@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat? + +Yes. Check the @file{doc/examples} directory in the source +repository, also available online at: +@url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}. + +Examples are also installed by default, usually in +@code{$PREFIX/share/ffmpeg/examples}. + +Also you may read the Developers Guide of the FFmpeg documentation. Alternatively, +examine the source code for one of the many open source projects that +already incorporate FFmpeg 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 FFmpeg 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 FFmpeg in object-oriented C++? + +FFmpeg 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 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 stripped to create ffmpeg, ffplay, etc. If +you need the debug information, use the *_g versions. + +@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 FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves. + +FFmpeg builds static libraries by default. In static libraries, dependencies +are not handled. That has two consequences. First, you must specify the +libraries in dependency order: @code{-lavdevice} must come before +@code{-lavformat}, @code{-lavutil} must come after everything else, etc. +Second, external libraries that are used in FFmpeg have to be specified too. + +An easy way to get the full list of required libraries in dependency order +is to use @code{pkg-config}. + +@example + c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec) +@end example + +See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for +more details. + +@section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available. + +FFmpeg 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 FFmpeg includes using @code{extern "C"}. + +See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3} + +@section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope + +FFmpeg 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 have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat? + +You have to create a custom AVIOContext using @code{avio_alloc_context}, +see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources. + +@section Where can I find libav* headers for Pascal/Delphi? + +see @url{http://www.iversenit.dk/dev/ffmpeg-headers/} + +@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm? + +see @url{http://www.ffmpeg.org/~michael/} + +@section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec? + +Even if peculiar since it is network oriented, RTP is a container like any +other. You have to @emph{demux} RTP before feeding the payload to libavcodec. +In this specific case please look at RFC 4629 to see how it should be done. + +@section AVStream.r_frame_rate is wrong, it is much larger than the frame rate. + +r_frame_rate is NOT the average frame rate, it is the smallest frame rate +that can accurately represent all timestamps. So no, it is not +wrong if it is larger than the average! +For example, if you have mixed 25 and 30 fps content, then r_frame_rate +will be 150. + +@section Why is @code{make fate} not running all tests? + +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 Why is @code{make fate} not finding the samples? + +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 |