1. General Problems

1.1 I cannot read this file although this format seems to be supported by ffmpeg.

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.

1.2 How do I encode JPEGs to another format ?

If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:

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

`%d' is replaced by the image number.

`img%03d.jpg' generates `img001.jpg', `img002.jpg', etc...

The same system is used for the other image formats.

1.3 FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?

No. FFmpeg only supports open source codecs. Windows DLLs are not portable, bloated and often slow.

1.4 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's quite logical that there is a small reduction of quality. This is not a bug.

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

Use `-' as filename.

1.6 Why does ffmpeg not decode audio in VOB files ?

The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg as the component that handles AC3 decoding (liba52) is currently released under the GPL. If you have liba52 installed on your system, enable AC3 decoding with ./configure --enable-a52. Take care: by enabling AC3, you automatically change the license of libavcodec from LGPL to GPL.

1.7 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:

`msmpeg4v2'

.avi/.asf

`msmpeg4'

.asf only

`wmv1'

.asf only

`wmv2'

.asf only

`mpeg4'

only if you have some MPEG-4 codec installed like ffdshow or XviD

`mpeg1'

.mpg only

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:

`adpcm_ima_wav'

`adpcm_ms'

`pcm'

`mp3'

if some MP3 codec like LAME is installed

1.8 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 (http://mplayerhq.hu/~michael/bttv-420-2.4.26.patch). This may also apply cleanly to other 2.4-series kernels.

1.9 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 (http://mplayerhq.hu/~michael/bttv-comb-2.4.26.patch) or (http://mplayerhq.hu/~michael/bttv-comb-2.6.6.patch) and pass 'combfilter=2'.

1.10 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".

1.11 -f jpeg doesn't work.

Try '-f image -img jpeg test%d.jpg'.

1.12 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.

1.13 ffmpeg does not work; What is wrong?

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

1.14 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.

1.15 How do I encode videos which play on the iPod?

`needed stuff'

-acodec aac -vcodec mpeg4 width<=320 height<=240

`working stuff'

4mv, title

`non-working stuff'

B-frames

`example command line'

ffmpeg -i input -acodec aac -ab 128 -vcodec mpeg4 -b 1200 -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 320x180 -title X output.mp4

1.16 How do I encode videos which play on the PSP?

`needed stuff'

-acodec aac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp

`working stuff'

4mv, title

`non-working stuff'

B-frames

`example command line'

ffmpeg -i input -acodec aac -ab 128 -vcodec mpeg4 -b 1200 -ar 24000 -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp output.mp4

`needed stuff for H.264'

-acodec aac -vcodec h264 width*height<=76800 width%16=0? height%16=0? -ar 48000 -coder 1 -r 30000/1001 or 15000/1001 -f psp

`working stuff for H.264'

title, loop filter

`non-working stuff for H.264'

CAVLC

`example command line'

ffmpeg -i input -acodec aac -ab 128 -vcodec h264 -b 1200 -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

2. Development

2.1 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.

2.2 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.

2.3 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 (projects.php).

2.4 Can you support my C compiler XXX ?

No. Only GCC is supported. GCC is ported to most systems available and there is no need to pollute the source code with #ifdefs related to the compiler.

2.5 Can I use FFmpeg or libavcodec under Windows ?

Yes, but the MinGW tools must be used to compile FFmpeg. You can link the resulting DLLs with any other Windows program. Read the Native Windows Compilation and Visual C++ compatibility sections in the FFmpeg documentation to find more information.

2.6 Can you add automake, libtool or autoconf support ?

No. These tools are too bloated and they complicate the build. Moreover, since only `gcc' is supported they would add little advantages in terms of portability.

2.7 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 (http://lkml.org/faq/lkmlfaq-15.html).

2.8 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.

2.9 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.

2.10 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.

2.11 Visual C++ produces many errors.

Visual C++ is not compliant to the C standard and does not support the inline assembly used in FFmpeg. If you wish - for whatever weird reason - to use Visual C++ for your project then you can link the Visual C++ code with libav* as long as you compile the latter with a working C compiler. For more information, see the Visual C++ compatibility section in the FFmpeg documentation.

There have been efforts to make FFmpeg compatible with Visual C++ in the past. However, they have all been rejected as too intrusive, especially since MinGW does the job perfectly adequately. None of the core developers work with Visual C++ and thus this item is low priority. Should you find the silver bullet that solves this problem, feel free to shoot it at us.

2.12 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.

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