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authorTim Redfern <tim@eclectronics.org>2014-02-17 13:36:38 +0000
committerTim Redfern <tim@eclectronics.org>2014-02-17 13:36:38 +0000
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-\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 aresample}. 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{aformat} explicitly in the filtergraph,
-specifying the exact format.
-
-@example
-aformat=sample_fmts=s16:channel_layouts=stereo
-@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 @command{ffmpeg_g}, @command{ffplay_g}, etc. which
-contain full debug information. Those binaries are stripped to create
-@command{ffmpeg}, @command{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 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.
-
-@code{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 @code{r_frame_rate}
-will be 150 (it is the least common multiple).
-If you are looking for the average frame rate, see @code{AVStream.avg_frame_rate}.
-
-@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