FFmpeg FAQ

1 General Questions

1.1 Why doesn’t FFmpeg support feature [xyz]?

Because no one has taken on that task yet. FFmpeg development isdriven by the tasks that are important to the individual developers.If there is a feature that is important to you, the best way to getit implemented is to undertake the task yourself or sponsor a developer.

1.2 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.

1.3 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 itscodecs. Please consult the supported codec list in the ffmpegdocumentation.

1.4 Which codecs are supported by Windows?

Windows does not support standard formats like MPEG very well, unless youinstall some additional codecs.

The following list of video codecs should work on most Windows systems:

msmpeg4v2: .avi/.asf
msmpeg4: .asf only
wmv1: .asf only
wmv2: .asf only
mpeg4: Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
mpeg1video: .mpg only

Note, ASF files often have .wmv or .wma extensions in Windows. It should alsobe mentioned that Microsoft claims a patent on the ASF format, and may sueor threaten users who create ASF files with non-Microsoft software. It isstrongly advised to avoid ASF where possible.

The following list of audio codecs should work on most Windows systems:

adpcm_ima_wav
adpcm_ms
pcm_s16le: always
libmp3lame: If some MP3 codec like LAME is installed.

2 Compilation

2.1 `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 tothe 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 ornot a bug they should fix:http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203.Then again, some of them do not know the difference between an undecidableproblem and an NP-hard problem...

2.2 I have installed this library with my distro’s package manager. Why does `configure` not see it?

Distributions usually split libraries in several packages. The main packagecontains the files necessary to run programs using the library. Thedevelopment package contains the files necessary to build programs using thelibrary. Sometimes, docs and/or data are in a separate package too.

To build FFmpeg, you need to install the development package. It is usuallycalled libfoo-dev or libfoo-devel. You can remove it after thebuild is finished, but be sure to keep the main package.

3 Usage

3.1 ffmpeg does not work; what is wrong?

Try a make distclean in the ffmpeg source directory before the build.If this does not help see(http://ffmpeg.org/bugreports.html).

3.2 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:

ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg

Notice that ‘%d’ is replaced by the image number.

img%03d.jpg means the sequence img001.jpg, img002.jpg, etc.

Use the -start_number option to declare a starting number forthe sequence. This is useful if your sequence does not start withimg001.jpg but is still in a numerical order. The followingexample will start with img100.jpg:

ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg

If you have large number of pictures to rename, you can use thefollowing command to ease the burden. The command, using the bourneshell syntax, symbolically links all files in the current directorythat match *jpg to the /tmp directory in the sequence ofimg001.jpg, img002.jpg and so on.

x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done

If you want to sequence them by oldest modified first, substitute$(ls -r -t *jpg) in place of *jpg.

Then run:

ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg

The same logic is used for any image format that ffmpeg reads.

You can also use cat to pipe images to ffmpeg:

cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg

3.3 How do I encode movie to single pictures?

Use:

ffmpeg -i movie.mpg movie%d.jpg

The movie.mpg used as input will be converted tomovie1.jpg, movie2.jpg, etc...

Instead of relying on file format self-recognition, you may also use

-c:v ppm
-c:v png
-c:v mjpeg

to force the encoding.

Applying that to the previous example:

ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg

Beware that there is no "jpeg" codec. Use "mjpeg" instead.

3.4 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’squite logical that there is a small reduction of quality. This is not a bug.

3.5 How can I read from the standard input or write to the standard output?

Use - as file name.

3.6 -f jpeg doesn’t work.

Try ’-f image2 test%d.jpg’.

3.7 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.

3.8 How do I encode Xvid or DivX video with ffmpeg?

Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4standard (note that there are many other coding formats that use thissame standard). Thus, use ’-c:v mpeg4’ to encode in these formats. Thedefault fourcc stored in an MPEG-4-coded file will be ’FMP4’. If you wanta different fourcc, use the ’-vtag’ option. E.g., ’-vtag xvid’ willforce the fourcc ’xvid’ to be stored as the video fourcc rather than thedefault.

3.9 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’.

3.10 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.

3.11 Interlaced video looks very bad when encoded with ffmpeg, what is wrong?

You should use ’-flags +ilme+ildct’ and maybe ’-flags +alt’ for interlacedmaterial, and try ’-top 0/1’ if the result looks really messed-up.

3.12 How can I read DirectShow files?

If you have built FFmpeg with ./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 ...

DirectShowSource("C:\path to your file\yourfile.asf")

... and then feed that text file to ffmpeg:

ffmpeg -i input.avs

For ANY other help on AviSynth, please visit theAviSynth homepage.

3.13 How can I join video files?

To "join" video files is quite ambiguous. The following list explains thedifferent kinds of "joining" and points out how those are addressed inFFmpeg. To join video files may mean:

To put them one after the other: this is called to concatenate them(in short: concat) and is addressedin this very faq.
To put them together in the same file, to let the user choose between thedifferent versions (example: different audio languages): this is called tomultiplex them together (in short: mux), and is done by simplyinvoking ffmpeg with several -i options.
For audio, to put all channels together in a single stream (example: twomono streams into one stereo stream): this is sometimes called tomerge them, and can be done using theamerge filter.
For audio, to play one on top of the other: this is called to mixthem, and can be done by first merging them into a single stream and thenusing the pan filter to mixthe channels at will.
For video, to display both together, side by side or one on top of a part ofthe other; it can be done using theoverlay video filter.

3.14 How can I concatenate video files?

There are several solutions, depending on the exact circumstances.

3.14.1 Concatenating using the concat filter

FFmpeg has a concat filter designed specifically for that, with examples in thedocumentation. This operation is recommended if you need to re-encode.

3.14.2 Concatenating using the concat demuxer

FFmpeg has a concat demuxer which you can use when you want to avoid a re-encode andyour format doesn’t support file level concatenation.

3.14.3 Concatenating using the concat protocol (file level)

FFmpeg has a concat protocol designed specifically for that, with examples in thedocumentation.

A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenatevideo by merely concatenating the files containing them.

Hence you may concatenate your multimedia files by first transcoding them tothese privileged formats, then using the humble cat command (or theequally humble copy under Windows), and finally transcoding back to yourformat of choice.

ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpgffmpeg -i input2.avi -qscale:v 1 intermediate2.mpgcat intermediate1.mpg intermediate2.mpg > intermediate_all.mpgffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi

Additionally, you can use the concat protocol instead of cat orcopy which will avoid creation of a potentially huge intermediate file.

ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpgffmpeg -i input2.avi -qscale:v 1 intermediate2.mpgffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpgffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi

Note that you may need to escape the character "|" which is special for manyshells.

Another option is usage of named pipes, should your platform support it:

mkfifo intermediate1.mpgmkfifo intermediate2.mpgffmpeg -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

3.14.4 Concatenating using raw audio and video

Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs alsoallow concatenation, and the transcoding step is almost lossless.When using multiple yuv4mpegpipe(s), the first line needs to be discardedfrom all but the first stream. This can be accomplished by piping throughtail as seen below. Note that when piping through tail youmust use command grouping, { ;}, to background properly.

For example, let’s say we want to concatenate two FLV files into anoutput.flv file:

mkfifo temp1.amkfifo temp1.vmkfifo temp2.amkfifo temp2.vmkfifo all.amkfifo all.vffmpeg -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.flvrm temp[12].[av] all.[av]

3.15 Using `-f lavfi`, audio becomes mono for no apparent reason.

Use -dumpgraph - to find out exactly where the channel layout islost.

Most likely, it is through auto-inserted aresample. Try to understandwhy the converting filter was needed at that place.

Just before the output is a likely place, as -f lavfi currentlyonly support packed S16.

Then insert the correct aformat explicitly in the filtergraph,specifying the exact format.

aformat=sample_fmts=s16:channel_layouts=stereo

3.16 Why does FFmpeg not see the subtitles in my VOB file?

VOB and a few other formats do not have a global header that describeseverything present in the file. Instead, applications are supposed to scanthe file to see what it contains. Since VOB files are frequently large, onlythe beginning is scanned. If the subtitles happen only later in the file,they will not be initially detected.

Some applications, including the ffmpeg command-line tool, can onlywork with streams that were detected during the initial scan; streams thatare detected later are ignored.

The size of the initial scan is controlled by two options: probesize(default ~5? Mo) and analyzeduration (default 5,000,000? ?μs = 5? s). Forthe subtitle stream to be detected, both values must be large enough.

3.17 Why was the `ffmpeg` `-sameq` option removed? What to use instead?

The -sameq option meant "same quantizer", and made sense only in avery 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 hadroughly the expected visible effect, but achieved it in a very inefficientway.

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 apoint acceptable for your tastes. The most common options to do that are-qscale and -qmax, but you should peruse the documentationof the encoder you chose.

4 Development

4.1 Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?

Yes. Check the doc/examples directory in the sourcerepository, also available online at:https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples.

Examples are also installed by default, usually in$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 thatalready incorporate FFmpeg at (projects.html).

4.2 Can you support my C compiler XXX?

It depends. If your compiler is C99-compliant, then patches to supportit are likely to be welcome if they do not pollute the source codewith #ifdefs related to the compiler.

4.3 Is Microsoft Visual C++ supported?

Yes. Please see the Microsoft Visual C++section in the FFmpeg documentation.

4.4 Can you add automake, libtool or autoconf support?

No. These tools are too bloated and they complicate the build.

4.5 Why not rewrite FFmpeg in object-oriented C++?

FFmpeg is already organized in a highly modular manner and does not need tobe rewritten in a formal object language. Further, many of the developersfavor straight C; it works for them. For more arguments on this matter,read "Programming Religion".

4.6 Why are the ffmpeg programs devoid of debugging symbols?

The build process creates ffmpeg_g, ffplay_g, etc. whichcontain full debug information. Those binaries are stripped to createffmpeg, ffplay, etc. If you need the debug information, usethe *_g versions.

4.7 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 placedunder #if CONFIG_GPL without breaking anything. So, for example, a new codecor filter would be OK under GPL while a bug fix to LGPL code would not.

4.8 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, dependenciesare not handled. That has two consequences. First, you must specify thelibraries in dependency order: -lavdevice must come before-lavformat, -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 orderis to use pkg-config.

c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec)

See doc/example/Makefile and doc/example/pc-uninstalled formore details.

4.9 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++ applicationyou need to explicitly state that you are using a C library. You can do this byencompassing your FFmpeg includes using extern "C".

See http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3

4.10 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

4.11 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 avio_alloc_context,see libavformat/aviobuf.c in FFmpeg and libmpdemux/demux_lavf.c in MPlayer or MPlayer2 sources.

4.12 Where is the documentation about ffv1, msmpeg4, asv1, 4xm?

see http://www.ffmpeg.org/~michael/

4.13 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 anyother. You have to demux RTP before feeding the payload to libavcodec.In this specific case please look at RFC 4629 to see how it should be done.

4.14 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 ratethat can accurately represent all timestamps. So no, it is notwrong if it is larger than the average!For example, if you have mixed 25 and 30 fps content, then r_frame_ratewill be 150 (it is the least common multiple).If you are looking for the average frame rate, see AVStream.avg_frame_rate.

4.15 Why is `make fate` not running all tests?

Make sure you have the fate-suite samples and the SAMPLES Make variableor FATE_SAMPLES environment variable or the --samplesconfigure option is set to the right path.

4.16 Why is `make fate` not finding the samples?

Do you happen to have a ~ character in the samples path to indicate ahome directory? The value is used in ways where the shell cannot expand it,causing FATE to not find files. Just replace ~ by the full path.

This document was generated on November 29, 2014 using makeinfo.

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