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