faq.texi

\input texinfo @c -*- texinfo -*-

@settitle FFmpeg FAQ
@titlepage
@sp 7
@center @titlefont{FFmpeg FAQ}
@sp 3
@end titlepage


@chapter General Problems

@section ffserver doesn't 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.

@section I cannot read this file although this format seems to be suppored 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.

@section I get audio/video synchro problems when grabbing.

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

@section How do I encode jpegs to another format ?

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

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

@samp{%d} is replaced by the image number.

@file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...

The same system is used for the other image formats.

@section 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.

@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 its
quite logic 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 filename.

@section Why Audio is not decoded in VOB files ?

AC3 decoding is optional as the codec is currently released under the
GPL. Enable it with @code{./configure --enable-a52}. Take care: by
enabling AC3, you automatically change the license of libavcodec from
LGPL to GPL.

@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 mpeg4 codec installed like ffdshow or xvid
@item mpeg1
.mpg only
@end table
note, asf often uses .wmv or .wma extensions in windows, it should also be
mentioned that asf is patented, so microsoft may sue or threaten users who
use it if they see any reason to do so, it is strongly recommanded to avoid asf
for any use

The following list of audio codecs should work on most windows systems
@table @option
@item adpcm_ima_wav
@item adpcm_ms
@item pcm
@item mp3
if some mp3 codec like lame is installed
@end table

@section The chrominance seems to come from a different time then the luminance on bt8x8 captures on linux?

well known bug in the bt8x8 driver, for 2.4.26 theres a patch at 
(@url{http://www.mplayerhq.hu/~michael/bttv-420-2.4.26.patch}), i suspect that
this will also apply cleanly to other 2.4 kernels

@section How to avoid the ugly aliassing artefacts 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 too apply (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
or (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
and pass 'combfilter=2'

@section 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 are lucky and
will become the first person in history to get a different awnser from "upgrade
to cvs".

@section -f jpeg doesnt work.

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

@section i cant change the framerate

some codecs, like mpeg1/2 only allow a small number of fixed framerates, 
choose a different codec with -vcodec

@chapter Development

@section Are there examples of use of the FFmpeg libraries libavcodec and libavformat ?

Yes. Read the Developers Guide of the FFmpeg documentation.

@section Can you support my C compiler XXX ?

No. Only GCC is supported. GCC is ported on most systems available and I
don't see the need to pollute the source code with @code{#ifdef}s
related to the compiler.

@section Can I use FFmpeg or libavcodec under Windows ?

Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
can link the resulting DLLs with any other Windows program. Read the
@emph{Native Windows Compilation} section in the FFmpeg documentation
to have more information.

@section Can you add automake, libtool or autoconf support ?

No. These tools are too blowted and they complicate the build. Moreover,
since only @samp{gcc} is supported they would add little advantages in
terms of portability.

@section ffmpeg doesnt contain any debugging symbols ?

try ffmpeg_g, ffplay_g, ...

@bye