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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 one 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 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 initially 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
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