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diff --git a/contrib/ffmpeg/doc/faq.texi b/contrib/ffmpeg/doc/faq.texi new file mode 100644 index 000000000..85a0915b9 --- /dev/null +++ b/contrib/ffmpeg/doc/faq.texi @@ -0,0 +1,472 @@ +\input texinfo @c -*- texinfo -*- + +@settitle FFmpeg FAQ +@titlepage +@sp 7 +@center @titlefont{FFmpeg FAQ} +@sp 3 +@end titlepage + + +@chapter General Questions + +@section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between? + +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. + +@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". + +@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 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 + +@section Is there a forum for FFmpeg? I do not like mailing lists. + +Yes, (@url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user}). + +@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 installed like ffdshow or XviD +@item mpeg1 +.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 +@item mp3 +if some MP3 codec like LAME is installed +@end table + + +@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 to 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... + +The same logic is used for any image format that ffmpeg reads. + +@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 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. + +@section How can I read from the standard input or write to the standard output? + +Use @file{-} as filename. + +@section Why does FFmpeg not decode audio in VOB files? + +The audio is AC-3 (a.k.a. A/52). AC-3 decoding is an optional component in FFmpeg +as the component that handles AC-3 decoding is currently released under the GPL. +Enable AC-3 decoding with @code{./configure --enable-gpl}. Take care: By +enabling AC-3, you automatically change the license of libavcodec from +LGPL to GPL. + +@section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux? + +This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at +(@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-420-2.4.26.patch?view=co}). This may also +apply cleanly to other 2.4-series kernels. + +@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux? + +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://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.4.26.patch?view=co}) +or (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co}) +and pass 'combfilter=2'. + +@section -f jpeg doesn't work. + +Try '-f image2 test%d.jpg'. + +@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. + +@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 '-vcodec mpeg4' to encode 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 libfaac -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 libfaac -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 libfaac -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 libfaac -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 libfaac -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 libfaac -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', +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' +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? + +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. +(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: +@example + ffmpeg -i input.avs +@end example + +For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}. + +@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 +ffmpeg -i input1.avi -sameq intermediate1.mpg +ffmpeg -i input2.avi -sameq intermediate2.mpg +cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg +ffmpeg -i intermediate_all.mpg -sameq output.avi +@end example + +Notice that you should either use @code{-sameq} 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 +ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null & +ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null & +cat intermediate1.mpg intermediate2.mpg |\ +ffmpeg -f mpeg -i - -sameq -vcodec 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. + +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 +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 - > temp2.v < /dev/null & +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 \ + -sameq -y output.flv +rm temp[12].[av] all.[av] +@end example + +@section FFmpeg does not adhere to the -maxrate setting, some frames are bigger than maxrate/fps. + +Read the MPEG spec about video buffer verifier. + +@section I want CBR, but no matter what I do frame sizes differ. + +You do not understand what CBR is, please read the MPEG spec. +Read about video buffer verifier and constant bitrate. +The one sentence summary is that there is a buffer and the input rate is +constant, the output can vary as needed. + +@section How do I check if a stream is CBR? + +To quote the MPEG-2 spec: +"There is no way to tell that a bitstream is constant bitrate without +examining all of the vbv_delay values and making complicated computations." + + +@chapter Development + +@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat? + +Yes. 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? + +No. Microsoft Visual C++ is not compliant to the C99 standard and does +not - among other things - support the inline assembly used in FFmpeg. +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{Microsoft Visual C++ compatibility} section in the FFmpeg +documentation. + +There have been efforts to make FFmpeg compatible with MSVC++ in the +past. However, they have all been rejected as too intrusive, especially +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. + +We strongly recommend you to move over from MSVC++ to MinGW tools. + +@section Can I use FFmpeg or libavcodec under Windows? + +Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg. +Read the @emph{Windows} section in the FFmpeg documentation to find more +information. + +To get help and instructions for building FFmpeg under Windows, check out +the FFmpeg Windows Help Forum at +@url{http://arrozcru.no-ip.org/ffmpeg/}. + +@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 "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}). + +@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? + +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. + +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 libavcodec 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 have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat? + +You have to implement a URLProtocol, see libavformat/file.c in FFmpeg +and libmpdemux/demux_lavf.c in MPlayer sources. + +@section I get "No compatible shell script interpreter found." in MSys. + +The standard MSys bash (2.04) is broken. You need to install 2.05 or later. + +@section I get "./configure: line <xxx>: pr: command not found" in MSys. + +The standard MSys install doesn't come with pr. You need to get it from the coreutils package. + +@section I tried to pass RTP packets into a decoder, but it doesn't work. + +RTP is a container format like any other, you must first depacketize the +codec frames/samples stored in RTP and then feed to the decoder. + +@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://svn.mplayerhq.hu/michael/trunk/docs/} + +@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 framerate. + +r_frame_rate is NOT the average framerate, it is the smallest framerate +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. + +@bye |