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[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
87759af9 19@section How do I encode JPEGs to another format ?
7ff56c72 20
87759af9 21If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:
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22
23@example
a9d21e78 24 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
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25@end example
26
27@samp{%d} is replaced by the image number.
28
29@file{img%03d.jpg} generates @file{img001.jpg}, @file{img002.jpg}, etc...
30
31The same system is used for the other image formats.
32
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33(Note: you need -f image2 for all image formats except GIF; see next section).
34
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35@section Only GIF is listed by -format. Is that the only accepted image format?
36
37No, there are more; they are listed among the video codecs:
38 jpeg, png, ppm, pbm, pam, pgm.
39
40For example:
41@example
42 ffmpeg -f image2 -i menu.png -f image2 menu.jpg
43@end example
44
45The @file{menu.png} used as input will be converted to @file{menu.jpg}.
46
47Instead of relying on file format self-recognition, you may also use
48@table @option
49@item -vcodec ppm
50@item -vcodec png
51@item -vcodec mjpeg
52@end table
53to force the encoding.
54
55Applying that to the previous example:
56@example
57 ffmpeg -f image2 -vcodec png -i menu.png -f image2 -vcodec mjpeg menu.jpg
58@end example
59
60Beware that there is no "jpeg" codec. Use "mjpeg" instead.
61
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62@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
63
64No. FFmpeg only supports open source codecs. Windows DLLs are not
65portable, bloated and often slow.
66
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67@section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem ?
68
69This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work.
70
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71@section Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
72
73For multithreaded MPEG* encoding, the encoded slices must be independent,
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74otherwise thread n would practically have to wait for n-1 to finish, so it's
75quite logical that there is a small reduction of quality. This is not a bug.
f2fe8752 76
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77@section How can I read from the standard input or write to the standard output ?
78
79Use @file{-} as filename.
80
cacf7199 81@section Why does ffmpeg not decode audio in VOB files ?
db0e9b03 82
cacf7199 83The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
115329f1 84as the component that handles AC3 decoding (liba52) is currently released under
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85the GPL. If you have liba52 installed on your system, enable AC3 decoding
86with @code{./configure --enable-a52}. Take care: by
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87enabling AC3, you automatically change the license of libavcodec from
88LGPL to GPL.
89
87759af9 90@section Which codecs are supported by Windows ?
c75f51f6 91
115329f1 92Windows does not support standard formats like MPEG very well, unless you
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93install some additional codecs
94
9ba42958 95The following list of video codecs should work on most Windows systems:
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96@table @option
97@item msmpeg4v2
98.avi/.asf
99@item msmpeg4
100.asf only
101@item wmv1
102.asf only
103@item wmv2
104.asf only
105@item mpeg4
9ba42958 106only if you have some MPEG-4 codec installed like ffdshow or XviD
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107@item mpeg1
108.mpg only
109@end table
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110Note, ASF files often have .wmv or .wma extensions in Windows. It should also
111be mentioned that Microsoft claims a patent on the ASF format, and may sue
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112or threaten users who create ASF files with non-Microsoft software. It is
113strongly advised to avoid ASF where possible.
c75f51f6 114
9ba42958 115The following list of audio codecs should work on most Windows systems:
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116@table @option
117@item adpcm_ima_wav
118@item adpcm_ms
119@item pcm
120@item mp3
9ba42958 121if some MP3 codec like LAME is installed
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122@end table
123
9ba42958 124@section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
7c0dc383 125
115329f1 126This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
70b0bb87 127(@url{http://mplayerhq.hu/~michael/bttv-420-2.4.26.patch}). This may also
cacf7199 128apply cleanly to other 2.4-series kernels.
7c0dc383 129
87759af9 130@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
7c0dc383 131
cacf7199 132Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
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133will cause somewhat too strong filtering. A fix is to apply (@url{http://mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
134or (@url{http://mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
cacf7199 135and pass 'combfilter=2'.
7c0dc383 136
9ba42958 137@section I have a problem with an old version of ffmpeg; where should I report it?
cacf7199 138Nowhere. Upgrade to the latest release or if there is no recent release upgrade
1c1b5a40 139to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
87759af9 140become the first person in history to get an answer different from "upgrade
1c1b5a40 141to Subversion HEAD".
dd1368db 142
9ba42958 143@section -f jpeg doesn't work.
fc3e9202 144
a9d21e78 145Try '-f image2 test%d.jpg'.
fc3e9202 146
cacf7199 147@section Why can I not change the framerate?
73468318 148
9ba42958 149Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
cacf7199 150Choose a different codec with the -vcodec command line option.
73468318 151
cacf7199 152@section ffmpeg does not work; What is wrong?
9291d591 153
cacf7199 154Try a 'make distclean' in the ffmpeg source directory. If this does not help see
7a771569 155(@url{http://ffmpeg.org/bugreports.php}).
9291d591 156
87759af9 157@section How do I encode XviD or DivX video with ffmpeg?
f62e9435 158
87759af9 159Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
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160standard (note that there are many other coding formats that use this
161same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
c9a08db9 162default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
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163a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
164force the fourcc 'xvid' to be stored as the video fourcc rather than the
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165default.
166
18e7d87c 167@section How do I encode videos which play on the iPod?
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168
169@table @option
18e7d87c 170@item needed stuff
b4aead58 171-acodec aac -vcodec mpeg4 width<=320 height<=240
18e7d87c 172@item working stuff
b4aead58 1734mv, title
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174@item non-working stuff
175B-frames
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176@item example command line
177ffmpeg -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
178@end table
179
18e7d87c 180@section How do I encode videos which play on the PSP?
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181
182@table @option
18e7d87c 183@item needed stuff
b4aead58 184-acodec aac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
18e7d87c 185@item working stuff
b4aead58 1864mv, title
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187@item non-working stuff
188B-frames
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189@item example command line
190ffmpeg -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
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191@item needed stuff for H.264
192-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
193@item working stuff for H.264
194title, loop filter
195@item non-working stuff for H.264
196CAVLC
197@item example command line
198ffmpeg -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
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199@end table
200
99f6278e 201@section How can I read DirectShow files?
2c29781d 202
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203If you have built FFmpeg with @code{./configure --enable-avisynth}
204(only possible on MinGW/Cygwin platforms),
205then you may use any file that DirectShow can read as input.
206(Be aware that this feature has been recently added,
207so you will need to help yourself in case of problems.)
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208
209Just create an "input.avs" text file with this single line ...
210@example
211 DirectShowSource("C:\path to your file\yourfile.asf")
212@end example
99f6278e 213... and then feed that text file to FFmpeg:
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214@example
215 ffmpeg -i input.avs
216@end example
217
218For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
219
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220@chapter Development
221
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222@section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
223
224Like most open source projects FFmpeg suffers from a certain lack of
225manpower. For this reason the developers have to prioritize the work
226they do and putting out releases is not at the top of the list, fixing
227bugs and reviewing patches takes precedence. Please don't complain or
228request more timely and/or frequent releases unless you are willing to
229help out creating them.
230
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231@section Why doesn't FFmpeg support feature [xyz]?
232
233Because no one has taken on that task yet. FFmpeg development is
234driven by the tasks that are important to the individual developers.
235If there is a feature that is important to you, the best way to get
236it implemented is to undertake the task yourself.
237
238
cacf7199 239@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
a93b9dba 240
cacf7199 241Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
115329f1 242examine the source code for one of the many open source projects that
cacf7199 243already incorporate ffmpeg at (@url{projects.php}).
a93b9dba 244
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245@section Can you support my C compiler XXX ?
246
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247No. Only GCC is supported. GCC is ported to most systems available and there
248is no need to pollute the source code with @code{#ifdef}s
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249related to the compiler.
250
988a9f9e 251@section Can I use FFmpeg or libavcodec under Windows ?
7ff56c72 252
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253Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
254can link the resulting DLLs with any other Windows program. Read the
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255@emph{Native Windows Compilation} and @emph{Visual C++ compatibility}
256sections in the FFmpeg documentation to find more information.
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257
258@section Can you add automake, libtool or autoconf support ?
259
cacf7199 260No. These tools are too bloated and they complicate the build. Moreover,
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261since only @samp{gcc} is supported they would add little advantages in
262terms of portability.
263
cacf7199 264@section Why not rewrite ffmpeg in object-oriented C++ ?
fbf33e4f 265
87759af9 266ffmpeg is already organized in a highly modular manner and does not need to
115329f1 267be rewritten in a formal object language. Further, many of the developers
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268favor straight C; it works for them. For more arguments on this matter,
269read "Programming Religion" at (@url{http://lkml.org/faq/lkmlfaq-15.html}).
270
271@section Why are the ffmpeg programs devoid of debugging symbols ?
272
273The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
274information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
275you need the debug information, used the *_g versions.
fbf33e4f 276
e180129f 277@section I do not like the LGPL, can I contribute code under the GPL instead ?
61a1e081 278
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279Yes, as long as the code is optional and can easily and cleanly be placed
280under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
281or filter would be OK under GPL while a bugfix to LGPL code would not.
61a1e081 282
e180129f 283@section I want to compile xyz.c alone but my compiler produced many errors.
61a1e081 284
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285Common code is in its own files in libav* and is used by the individual
286codecs. They will not work without the common parts, you have to compile
287the whole libav*. If you wish, disable some parts with configure switches.
288You can also try to hack it and remove more, but if you had problems fixing
289the compilation failure then you are probably not qualified for this.
61a1e081 290
9fcfac15 291@section Visual C++ produces many errors.
61a1e081 292
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293Visual C++ is not compliant to the C standard and does not support
294the inline assembly used in FFmpeg.
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295If you wish - for whatever weird reason - to use Visual C++ for your
296project then you can link the Visual C++ code with libav* as long as
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297you compile the latter with a working C compiler. For more information, see
298the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
61a1e081 299
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300There have been efforts to make FFmpeg compatible with Visual C++ in the
301past. However, they have all been rejected as too intrusive, especially
302since MinGW does the job perfectly adequately. None of the core developers
303work with Visual C++ and thus this item is low priority. Should you find
304the silver bullet that solves this problem, feel free to shoot it at us.
305
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306@section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat ?
307
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308You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
309and libmpdemux/demux_lavf.c in MPlayer sources.
f994f61e 310
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311@section I get "No compatible shell script interpreter found." in MSys.
312
313The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
314
7ff56c72 315@bye