FFmpeg FAQ:

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# 1. General Problems

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## 1.1 ffserver does not work.

ffmpeg development is now concentrated on the codec and format handling. New developments broke ffserver, so don't expect it to work correctly. If you have time and experience, please help us fix it.

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## 1.2 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.

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## 1.3 I get audio/video synchronization problems when grabbing.

Currently, the grabbing stuff does not handle synchronisation correctly. You are free to correct it. A fix is planned.

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## 1.4 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.

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## 1.5 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.

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## 1.6 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.

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

Use ``-`' as filename.

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## 1.8 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.

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## 1.9 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 mpeg4 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

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## 1.10 Why does the chrominance data seem to be sampled at a different time than 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://www.mplayerhq.hu/~michael/bttv-420-2.4.26.patch). This may also apply cleanly to other 2.4-series kernels.

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## 1.11 How do I avoid the ugly aliassing 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://www.mplayerhq.hu/~michael/bttv-comb-2.4.26.patch) or (http://www.mplayerhq.hu/~michael/bttv-comb-2.6.6.patch) and pass 'combfilter=2'.

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## 1.12 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 cvs. You could also try to report it. Maybe you will get lucky and become the first person in history to get a different answer from "upgrade to cvs".

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## 1.13 -f jpeg doesnt work.

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

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## 1.14 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.

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## 1.15 ffmpeg does not work; What is wrong?

Try a 'make distclean' in the ffmpeg source directory. If this does not help see (ffmpeg-bugreport.html).

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## 1.16 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 a MPEG-4-coded file will be 'DIVX'. 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.

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# 2. Development

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## 2.1 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).

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## 2.2 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 `#ifdef`s related to the compiler.

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## 2.3 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 section in the FFmpeg documentation to find more information.

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## 2.4 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.

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## 2.5 Why not rewrite ffmpeg in object-oriented C++ ?

ffmpeg is already organized in a highly modular manner 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).

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## 2.6 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.

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# Table of Contents

> 1. General Problems

> > 1.1 ffserver does not work.
> > 1.2 I cannot read this file although this format seems to be supported by ffmpeg.
> > 1.3 I get audio/video synchronization problems when grabbing.
> > 1.4 How do I encode jpegs to another format ?
> > 1.5 FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
> > 1.6 Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
> > 1.7 How can I read from the standard input or write to the standard output ?
> > 1.8 Why does ffmpeg not decode audio in VOB files ?
> > 1.9 Which codecs are supported by windows ?
> > 1.10 Why does the chrominance data seem to be sampled at a different time than the luminance data on bt8x8 captures on Linux?
> > 1.11 How do I avoid the ugly aliassing artifacts in bt8x8 captures on linux?
> > 1.12 I have a problem with an old version of ffmpeg; where should i report it?
> > 1.13 -f jpeg doesnt work.
> > 1.14 Why can I not change the framerate?
> > 1.15 ffmpeg does not work; What is wrong?
> > 1.16 How do I encode XviD or DIVX video with ffmpeg?

> 2. Development

> > 2.1 Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
> > 2.2 Can you support my C compiler XXX ?
> > 2.3 Can I use FFmpeg or libavcodec under Windows ?
> > 2.4 Can you add automake, libtool or autoconf support ?
> > 2.5 Why not rewrite ffmpeg in object-oriented C++ ?
> > 2.6 Why are the ffmpeg programs devoid of debugging symbols ?

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# Short Table of Contents

> 1. General Problems
> 2. Development

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# About this document

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