[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 How do I encode JPEGs to another format ?
21 If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:
23 @example
24 ffmpeg -i img%d.jpg /tmp/a.mpg
25 @end example
27 @samp{%d} is replaced by the image number.
29 @file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...
31 The same system is used for the other image formats.
33 @section Only GIF is listed by -format. Is that the only accepted image format?
35 No, there are more; they are listed among the video codecs:
36 jpeg, png, ppm, pbm, pam, pgm.
38 For example:
39 @example
40 ffmpeg -f image2 -i menu.png -f image2 menu.jpg
41 @end example
43 The @file{menu.png} used as input will be converted to @file{menu.jpg}.
45 Instead of relying on file format self-recognition, you may also use
46 @table @option
47 @item -vcodec ppm
48 @item -vcodec png
49 @item -vcodec mjpeg
50 @end table
51 to force the encoding.
53 Applying that to the previous example:
54 @example
55 ffmpeg -f image2 -vcodec png -i menu.png -f image2 -vcodec mjpeg menu.jpg
56 @end example
58 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
60 @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
62 No. FFmpeg only supports open source codecs. Windows DLLs are not
63 portable, bloated and often slow.
65 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
67 For multithreaded MPEG* encoding, the encoded slices must be independent,
68 otherwise thread n would practically have to wait for n-1 to finish, so it's
69 quite logical that there is a small reduction of quality. This is not a bug.
71 @section How can I read from the standard input or write to the standard output ?
73 Use @file{-} as filename.
75 @section Why does ffmpeg not decode audio in VOB files ?
77 The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
78 as the component that handles AC3 decoding (liba52) is currently released under
79 the GPL. If you have liba52 installed on your system, enable AC3 decoding
80 with @code{./configure --enable-a52}. Take care: by
81 enabling AC3, you automatically change the license of libavcodec from
82 LGPL to GPL.
84 @section Which codecs are supported by Windows ?
86 Windows does not support standard formats like MPEG very well, unless you
87 install some additional codecs
89 The following list of video codecs should work on most Windows systems:
90 @table @option
91 @item msmpeg4v2
92 .avi/.asf
93 @item msmpeg4
94 .asf only
95 @item wmv1
96 .asf only
97 @item wmv2
98 .asf only
99 @item mpeg4
100 only if you have some MPEG-4 codec installed like ffdshow or XviD
101 @item mpeg1
102 .mpg only
103 @end table
104 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
105 be mentioned that Microsoft claims a patent on the ASF format, and may sue
106 or threaten users who create ASF files with non-Microsoft software. It is
107 strongly advised to avoid ASF where possible.
109 The following list of audio codecs should work on most Windows systems:
110 @table @option
111 @item adpcm_ima_wav
112 @item adpcm_ms
113 @item pcm
114 @item mp3
115 if some MP3 codec like LAME is installed
116 @end table
118 @section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
120 This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
121 (@url{http://mplayerhq.hu/~michael/bttv-420-2.4.26.patch}). This may also
122 apply cleanly to other 2.4-series kernels.
124 @section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
126 Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
127 will cause somewhat too strong filtering. A fix is to apply (@url{http://mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
128 or (@url{http://mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
129 and pass 'combfilter=2'.
131 @section I have a problem with an old version of ffmpeg; where should I report it?
132 Nowhere. Upgrade to the latest release or if there is no recent release upgrade
133 to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
134 become the first person in history to get an answer different from "upgrade
135 to Subversion HEAD".
137 @section -f jpeg doesn't work.
139 Try '-f image -img jpeg test%d.jpg'.
141 @section Why can I not change the framerate?
143 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
144 Choose a different codec with the -vcodec command line option.
146 @section ffmpeg does not work; What is wrong?
148 Try a 'make distclean' in the ffmpeg source directory. If this does not help see
149 (@url{http://ffmpeg.org/bugreports.php}).
151 @section How do I encode XviD or DivX video with ffmpeg?
153 Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
154 standard (note that there are many other coding formats that use this
155 same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
156 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
157 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
158 force the fourcc 'xvid' to be stored as the video fourcc rather than the
159 default.
161 @section How do I encode videos which play on the iPod?
163 @table @option
164 @item needed stuff
165 -acodec aac -vcodec mpeg4 width<=320 height<=240
166 @item working stuff
167 4mv, title
168 @item non-working stuff
169 B-frames
170 @item example command line
171 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
172 @end table
174 @section How do I encode videos which play on the PSP?
176 @table @option
177 @item needed stuff
178 -acodec aac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
179 @item working stuff
180 4mv, title
181 @item non-working stuff
182 B-frames
183 @item example command line
184 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
185 @item needed stuff for H.264
186 -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
187 @item working stuff for H.264
188 title, loop filter
189 @item non-working stuff for H.264
191 @item example command line
192 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
193 @end table
195 @chapter Development
197 @section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
199 Like most open source projects FFmpeg suffers from a certain lack of
200 manpower. For this reason the developers have to prioritize the work
201 they do and putting out releases is not at the top of the list, fixing
202 bugs and reviewing patches takes precedence. Please don't complain or
203 request more timely and/or frequent releases unless you are willing to
204 help out creating them.
206 @section Why doesn't FFmpeg support feature [xyz]?
208 Because no one has taken on that task yet. FFmpeg development is
209 driven by the tasks that are important to the individual developers.
210 If there is a feature that is important to you, the best way to get
211 it implemented is to undertake the task yourself.
214 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
216 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
217 examine the source code for one of the many open source projects that
218 already incorporate ffmpeg at (@url{projects.php}).
220 @section Can you support my C compiler XXX ?
222 No. Only GCC is supported. GCC is ported to most systems available and there
223 is no need to pollute the source code with @code{#ifdef}s
224 related to the compiler.
226 @section Can I use FFmpeg or libavcodec under Windows ?
228 Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
229 can link the resulting DLLs with any other Windows program. Read the
230 @emph{Native Windows Compilation} and @emph{Visual C++ compatibility}
231 sections in the FFmpeg documentation to find more information.
233 @section Can you add automake, libtool or autoconf support ?
235 No. These tools are too bloated and they complicate the build. Moreover,
236 since only @samp{gcc} is supported they would add little advantages in
237 terms of portability.
239 @section Why not rewrite ffmpeg in object-oriented C++ ?
241 ffmpeg is already organized in a highly modular manner and does not need to
242 be rewritten in a formal object language. Further, many of the developers
243 favor straight C; it works for them. For more arguments on this matter,
244 read "Programming Religion" at (@url{http://lkml.org/faq/lkmlfaq-15.html}).
246 @section Why are the ffmpeg programs devoid of debugging symbols ?
248 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
249 information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
250 you need the debug information, used the *_g versions.
252 @section I do not like the LGPL, can I contribute code under the GPL instead ?
254 Yes, as long as the code is optional and can easily and cleanly be placed
255 under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
256 or filter would be OK under GPL while a bugfix to LGPL code would not.
258 @section I want to compile xyz.c alone but my compiler produced many errors.
260 Common code is in its own files in libav* and is used by the individual
261 codecs. They will not work without the common parts, you have to compile
262 the whole libav*. If you wish, disable some parts with configure switches.
263 You can also try to hack it and remove more, but if you had problems fixing
264 the compilation failure then you are probably not qualified for this.
266 @section Visual C++ produces many errors.
268 Visual C++ is not compliant to the C standard and does not support
269 the inline assembly used in FFmpeg.
270 If you wish - for whatever weird reason - to use Visual C++ for your
271 project then you can link the Visual C++ code with libav* as long as
272 you compile the latter with a working C compiler. For more information, see
273 the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
275 There have been efforts to make FFmpeg compatible with Visual C++ in the
276 past. However, they have all been rejected as too intrusive, especially
277 since MinGW does the job perfectly adequately. None of the core developers
278 work with Visual C++ and thus this item is low priority. Should you find
279 the silver bullet that solves this problem, feel free to shoot it at us.
281 @section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat ?
283 You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
284 and libmpdemux/demux_lavf.c in MPlayer sources.
286 @bye