Add entry about release frequency.
[libav.git] / doc / faq.texi
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1\input texinfo @c -*- texinfo -*-
2
3@settitle FFmpeg FAQ
4@titlepage
5@sp 7
6@center @titlefont{FFmpeg FAQ}
7@sp 3
8@end titlepage
9
10
11@chapter General Problems
12
cacf7199 13@section I cannot read this file although this format seems to be supported by ffmpeg.
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14
15Even if ffmpeg can read the file format, it may not support all its
16codecs. Please consult the supported codec list in the ffmpeg
17documentation.
18
cacf7199 19@section I get audio/video synchronization problems when grabbing.
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20
21Currently, the grabbing stuff does not handle synchronisation
cacf7199 22correctly. You are free to correct it. A fix is planned.
7ff56c72 23
87759af9 24@section How do I encode JPEGs to another format ?
7ff56c72 25
87759af9 26If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:
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27
28@example
29 ffmpeg -i img%d.jpg /tmp/a.mpg
30@end example
31
32@samp{%d} is replaced by the image number.
33
34@file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...
35
36The same system is used for the other image formats.
37
38@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
39
40No. FFmpeg only supports open source codecs. Windows DLLs are not
41portable, bloated and often slow.
42
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43@section Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
44
45For multithreaded MPEG* encoding, the encoded slices must be independent,
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46otherwise thread n would practically have to wait for n-1 to finish, so it's
47quite logical that there is a small reduction of quality. This is not a bug.
f2fe8752 48
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49@section How can I read from the standard input or write to the standard output ?
50
51Use @file{-} as filename.
52
cacf7199 53@section Why does ffmpeg not decode audio in VOB files ?
db0e9b03 54
cacf7199 55The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
115329f1 56as the component that handles AC3 decoding (liba52) is currently released under
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57the GPL. If you have liba52 installed on your system, enable AC3 decoding
58with @code{./configure --enable-a52}. Take care: by
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59enabling AC3, you automatically change the license of libavcodec from
60LGPL to GPL.
61
87759af9 62@section Which codecs are supported by Windows ?
c75f51f6 63
115329f1 64Windows does not support standard formats like MPEG very well, unless you
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65install some additional codecs
66
9ba42958 67The following list of video codecs should work on most Windows systems:
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68@table @option
69@item msmpeg4v2
70.avi/.asf
71@item msmpeg4
72.asf only
73@item wmv1
74.asf only
75@item wmv2
76.asf only
77@item mpeg4
9ba42958 78only if you have some MPEG-4 codec installed like ffdshow or XviD
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79@item mpeg1
80.mpg only
81@end table
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82Note, ASF files often have .wmv or .wma extensions in Windows. It should also
83be mentioned that Microsoft claims a patent on the ASF format, and may sue
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84or threaten users who create ASF files with non-Microsoft software. It is
85strongly advised to avoid ASF where possible.
c75f51f6 86
9ba42958 87The following list of audio codecs should work on most Windows systems:
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88@table @option
89@item adpcm_ima_wav
90@item adpcm_ms
91@item pcm
92@item mp3
9ba42958 93if some MP3 codec like LAME is installed
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94@end table
95
9ba42958 96@section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
7c0dc383 97
115329f1 98This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
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99(@url{http://www.mplayerhq.hu/~michael/bttv-420-2.4.26.patch}). This may also
100apply cleanly to other 2.4-series kernels.
7c0dc383 101
87759af9 102@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
7c0dc383 103
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104Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
105will cause somewhat too strong filtering. A fix is to apply (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
fc3e9202 106or (@url{http://www.mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
cacf7199 107and pass 'combfilter=2'.
7c0dc383 108
9ba42958 109@section I have a problem with an old version of ffmpeg; where should I report it?
cacf7199 110Nowhere. Upgrade to the latest release or if there is no recent release upgrade
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111to CVS. You could also try to report it. Maybe you will get lucky and
112become the first person in history to get an answer different from "upgrade
113to CVS".
dd1368db 114
9ba42958 115@section -f jpeg doesn't work.
fc3e9202 116
87759af9 117Try '-f image -img jpeg test%d.jpg'.
fc3e9202 118
cacf7199 119@section Why can I not change the framerate?
73468318 120
9ba42958 121Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
cacf7199 122Choose a different codec with the -vcodec command line option.
73468318 123
cacf7199 124@section ffmpeg does not work; What is wrong?
9291d591 125
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126Try a 'make distclean' in the ffmpeg source directory. If this does not help see
127(@url{ffmpeg-bugreport.html}).
9291d591 128
87759af9 129@section How do I encode XviD or DivX video with ffmpeg?
f62e9435 130
87759af9 131Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
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132standard (note that there are many other coding formats that use this
133same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
c9a08db9 134default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
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135a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
136force the fourcc 'xvid' to be stored as the video fourcc rather than the
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137default.
138
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139@chapter Development
140
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141@section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
142
143Like most open source projects FFmpeg suffers from a certain lack of
144manpower. For this reason the developers have to prioritize the work
145they do and putting out releases is not at the top of the list, fixing
146bugs and reviewing patches takes precedence. Please don't complain or
147request more timely and/or frequent releases unless you are willing to
148help out creating them.
149
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150@section Why doesn't FFmpeg support feature [xyz]?
151
152Because no one has taken on that task yet. FFmpeg development is
153driven by the tasks that are important to the individual developers.
154If there is a feature that is important to you, the best way to get
155it implemented is to undertake the task yourself.
156
157
cacf7199 158@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
a93b9dba 159
cacf7199 160Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
115329f1 161examine the source code for one of the many open source projects that
cacf7199 162already incorporate ffmpeg at (@url{projects.php}).
a93b9dba 163
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164@section Can you support my C compiler XXX ?
165
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166No. Only GCC is supported. GCC is ported to most systems available and there
167is no need to pollute the source code with @code{#ifdef}s
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168related to the compiler.
169
988a9f9e 170@section Can I use FFmpeg or libavcodec under Windows ?
7ff56c72 171
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172Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
173can link the resulting DLLs with any other Windows program. Read the
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174@emph{Native Windows Compilation} and @emph{Visual C++ compatibility}
175sections in the FFmpeg documentation to find more information.
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176
177@section Can you add automake, libtool or autoconf support ?
178
cacf7199 179No. These tools are too bloated and they complicate the build. Moreover,
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180since only @samp{gcc} is supported they would add little advantages in
181terms of portability.
182
cacf7199 183@section Why not rewrite ffmpeg in object-oriented C++ ?
fbf33e4f 184
87759af9 185ffmpeg is already organized in a highly modular manner and does not need to
115329f1 186be rewritten in a formal object language. Further, many of the developers
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187favor straight C; it works for them. For more arguments on this matter,
188read "Programming Religion" at (@url{http://lkml.org/faq/lkmlfaq-15.html}).
189
190@section Why are the ffmpeg programs devoid of debugging symbols ?
191
192The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
193information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
194you need the debug information, used the *_g versions.
fbf33e4f 195
e180129f 196@section I do not like the LGPL, can I contribute code under the GPL instead ?
61a1e081 197
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198Yes, as long as the code is optional and can easily and cleanly be placed
199under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
200or filter would be OK under GPL while a bugfix to LGPL code would not.
61a1e081 201
e180129f 202@section I want to compile xyz.c alone but my compiler produced many errors.
61a1e081 203
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204Common code is in its own files in libav* and is used by the individual
205codecs. They will not work without the common parts, you have to compile
206the whole libav*. If you wish, disable some parts with configure switches.
207You can also try to hack it and remove more, but if you had problems fixing
208the compilation failure then you are probably not qualified for this.
61a1e081 209
9fcfac15 210@section Visual C++ produces many errors.
61a1e081 211
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212Visual C++ is not compliant to the C standard and does not support
213the inline assembly used in FFmpeg.
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214If you wish - for whatever weird reason - to use Visual C++ for your
215project then you can link the Visual C++ code with libav* as long as
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216you compile the latter with a working C compiler. For more information, see
217the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
61a1e081 218
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219There have been efforts to make FFmpeg compatible with Visual C++ in the
220past. However, they have all been rejected as too intrusive, especially
221since MinGW does the job perfectly adequately. None of the core developers
222work with Visual C++ and thus this item is low priority. Should you find
223the silver bullet that solves this problem, feel free to shoot it at us.
224
7ff56c72 225@bye