@end titlepage
-@chapter General Problems
+@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 bug report/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.
+
+You may view our mailing lists with a more forum-alike look here:
+@url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user},
+but, if you post, please remember that our mailing list rules still apply there.
+
+@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 ffserver doesn't not work.
+@section Which codecs are supported by Windows?
-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.
+Windows does not support standard formats like MPEG very well, unless you
+install some additional codecs.
-@section I cannot read this file although this format seems to be suppored by ffmpeg.
+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 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.
-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.
+The following list of audio codecs should work on most Windows systems:
+@table @option
+@item adpcm_ima_wav
+@item adpcm_ms
+@item pcm
+always
+@item mp3
+If some MP3 codec like LAME is installed.
+@end table
+
+
+@chapter Compilation
-@section I get audio/video synchro problems when grabbing.
+@section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}
-Currently, the grabbing stuff does not handle synchronisation
-correctly. You are free to correct it. It is planned to fix it ASAP.
+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.
-@section How do I encode jpegs to another format ?
+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...
-If the jpegs are named img1.jpg, img2.jpg, img3.jpg,..., use:
+@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 -i img%d.jpg /tmp/a.mpg
+ ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
@end example
-@samp{%d} is replaced by the image number.
+Notice that @samp{%d} is replaced by the image number.
-@file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...
+@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
-The same system is used for the other image formats.
+The same logic is used for any image format that ffmpeg reads.
-@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
+@section How do I encode movie to single pictures?
-No. FFmpeg only supports open source codecs. Windows DLLs are not
-portable, bloated and often slow.
+Use:
-@section How can I read from the standard input or write to the standard output ?
+@example
+ ffmpeg -i movie.mpg movie%d.jpg
+@end example
-Use @file{-} as filename.
+The @file{movie.mpg} used as input will be converted to
+@file{movie1.jpg}, @file{movie2.jpg}, etc...
-@section Why Audio is not decoded in VOB files ?
+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.
-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
+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 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 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 Which codecs are supported by windows ?
+@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.ffmpeg.org/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.ffmpeg.org/michael/trunk/patches/bttv-comb-2.4.26.patch?view=co})
+or (@url{http://svn.ffmpeg.org/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.
-Windows does not support standard formats like mpeg very well, unless you
-install some additional codecs
+@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 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?
-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 mpeg4 codec installed like ffdshow or xvid
-@item mpeg1
-.mpg only
+@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 -trellis 2 -aic 2 -cmp 2 -subcmp 2 -s 320x180 -title X output.mp4
@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
-The following list of audio codecs should work on most windows systems
+@section How do I encode videos which play on the PSP?
+
@table @option
-@item adpcm_ima_wav
-@item adpcm_ms
-@item pcm
-@item mp3
-if some mp3 codec like lame is installed
+@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 -trellis 2 -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 libx264 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 libx264 -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
+@item higher resolution for newer PSP firmwares, width<=480, height<=272
+-vcodec libx264 -level 21 -coder 1 -f psp
+@item example command line
+ffmpeg -i input -acodec libfaac -ab 128kb -ac 2 -ar 48000 -vcodec libx264 -level 21 -b 640kb -coder 1 -f psp -flags +loop -trellis 2 -partitions +parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 -g 250 -s 480x272 output.mp4
@end table
-@section The chrominance seems to come from a different time then the luminance on bt8x8 captures on linux?
+@section Which are good parameters for encoding high quality MPEG-4?
+
+'-mbd rd -flags +4mv+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.
+(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.
-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
+Read the MPEG spec about video buffer verifier.
-@section How to avoid the ugly aliassing artefacts in bt8x8 captures on linux?
+@section I want CBR, but no matter what I do frame sizes differ.
-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'
+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 -f jpeg doesnt work.
+@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."
-try '-f image -img jpeg test%d.jpg'
@chapter Development
-@section Are there examples of use of the FFmpeg libraries libavcodec and libavformat ?
+@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://ffmpeg.arrozcru.org/}.
+
+@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 stripped 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 #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 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.
-Yes. Read the Developers Guide of the FFmpeg documentation.
+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 Can you support my C compiler XXX ?
+@section Where can I find libav* headers for Pascal/Delphi?
-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.
+see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
-@section Can I use FFmpeg or libavcodec under Windows ?
+@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
-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.
+see @url{http://svn.ffmpeg.org/michael/trunk/docs/}
-@section Can you add automake, libtool or autoconf support ?
+@section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
-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.
+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 ffmpeg doesnt contain any debugging symbols ?
+@section AVStream.r_frame_rate is wrong, it is much larger than the framerate.
-try ffmpeg_g, ffplay_g, ...
+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
projects / ffmpeg / blobdiff