MSys bash 2.04 is broken.
[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 -f image2 -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 (Note: you need -f image2 for all image formats except GIF; see next section).
35 @section Only GIF is listed by -format. Is that the only accepted image format?
37 No, there are more; they are listed among the video codecs:
38 jpeg, png, ppm, pbm, pam, pgm.
40 For example:
41 @example
42 ffmpeg -f image2 -i menu.png -f image2 menu.jpg
43 @end example
45 The @file{menu.png} used as input will be converted to @file{menu.jpg}.
47 Instead 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
53 to force the encoding.
55 Applying 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
60 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
62 @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it ?
64 No. FFmpeg only supports open source codecs. Windows DLLs are not
65 portable, bloated and often slow.
67 @section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem ?
69 This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work.
71 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
73 For multithreaded MPEG* encoding, the encoded slices must be independent,
74 otherwise thread n would practically have to wait for n-1 to finish, so it's
75 quite logical that there is a small reduction of quality. This is not a bug.
77 @section How can I read from the standard input or write to the standard output ?
79 Use @file{-} as filename.
81 @section Why does ffmpeg not decode audio in VOB files ?
83 The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
84 as the component that handles AC3 decoding (liba52) is currently released under
85 the GPL. If you have liba52 installed on your system, enable AC3 decoding
86 with @code{./configure --enable-a52}. Take care: by
87 enabling AC3, you automatically change the license of libavcodec from
88 LGPL to GPL.
90 @section Which codecs are supported by Windows ?
92 Windows does not support standard formats like MPEG very well, unless you
93 install some additional codecs
95 The following list of video codecs should work on most Windows systems:
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
106 only if you have some MPEG-4 codec installed like ffdshow or XviD
107 @item mpeg1
108 .mpg only
109 @end table
110 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
111 be mentioned that Microsoft claims a patent on the ASF format, and may sue
112 or threaten users who create ASF files with non-Microsoft software. It is
113 strongly advised to avoid ASF where possible.
115 The following list of audio codecs should work on most Windows systems:
116 @table @option
117 @item adpcm_ima_wav
118 @item adpcm_ms
119 @item pcm
120 @item mp3
121 if some MP3 codec like LAME is installed
122 @end table
124 @section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
126 This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
127 (@url{}). This may also
128 apply cleanly to other 2.4-series kernels.
130 @section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
132 Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
133 will cause somewhat too strong filtering. A fix is to apply (@url{})
134 or (@url{})
135 and pass 'combfilter=2'.
137 @section I have a problem with an old version of ffmpeg; where should I report it?
138 Nowhere. Upgrade to the latest release or if there is no recent release upgrade
139 to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
140 become the first person in history to get an answer different from "upgrade
141 to Subversion HEAD".
143 @section -f jpeg doesn't work.
145 Try '-f image2 test%d.jpg'.
147 @section Why can I not change the framerate?
149 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
150 Choose a different codec with the -vcodec command line option.
152 @section ffmpeg does not work; What is wrong?
154 Try a 'make distclean' in the ffmpeg source directory. If this does not help see
155 (@url{}).
157 @section How do I encode XviD or DivX video with ffmpeg?
159 Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
160 standard (note that there are many other coding formats that use this
161 same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
162 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
163 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
164 force the fourcc 'xvid' to be stored as the video fourcc rather than the
165 default.
167 @section How do I encode videos which play on the iPod?
169 @table @option
170 @item needed stuff
171 -acodec aac -vcodec mpeg4 width<=320 height<=240
172 @item working stuff
173 4mv, title
174 @item non-working stuff
175 B-frames
176 @item example command line
177 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
178 @end table
180 @section How do I encode videos which play on the PSP?
182 @table @option
183 @item needed stuff
184 -acodec aac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
185 @item working stuff
186 4mv, title
187 @item non-working stuff
188 B-frames
189 @item example command line
190 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
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
194 title, loop filter
195 @item non-working stuff for H.264
197 @item example command line
198 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
199 @end table
201 @section How can I read DirectShow files?
203 If you have built FFmpeg with @code{./configure --enable-avisynth}
204 (only possible on MinGW/Cygwin platforms),
205 then you may use any file that DirectShow can read as input.
206 (Be aware that this feature has been recently added,
207 so you will need to help yourself in case of problems.)
209 Just create an "input.avs" text file with this single line ...
210 @example
211 DirectShowSource("C:\path to your file\yourfile.asf")
212 @end example
213 ... and then feed that text file to FFmpeg:
214 @example
215 ffmpeg -i input.avs
216 @end example
218 For ANY other help on Avisynth, please visit @url{}.
220 @chapter Development
222 @section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
224 Like most open source projects FFmpeg suffers from a certain lack of
225 manpower. For this reason the developers have to prioritize the work
226 they do and putting out releases is not at the top of the list, fixing
227 bugs and reviewing patches takes precedence. Please don't complain or
228 request more timely and/or frequent releases unless you are willing to
229 help out creating them.
231 @section Why doesn't FFmpeg support feature [xyz]?
233 Because no one has taken on that task yet. FFmpeg development is
234 driven by the tasks that are important to the individual developers.
235 If there is a feature that is important to you, the best way to get
236 it implemented is to undertake the task yourself.
239 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
241 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
242 examine the source code for one of the many open source projects that
243 already incorporate ffmpeg at (@url{projects.php}).
245 @section Can you support my C compiler XXX ?
247 No. Only GCC is supported. GCC is ported to most systems available and there
248 is no need to pollute the source code with @code{#ifdef}s
249 related to the compiler.
251 @section Can I use FFmpeg or libavcodec under Windows ?
253 Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
254 can link the resulting DLLs with any other Windows program. Read the
255 @emph{Native Windows Compilation} and @emph{Visual C++ compatibility}
256 sections in the FFmpeg documentation to find more information.
258 @section Can you add automake, libtool or autoconf support ?
260 No. These tools are too bloated and they complicate the build. Moreover,
261 since only @samp{gcc} is supported they would add little advantages in
262 terms of portability.
264 @section Why not rewrite ffmpeg in object-oriented C++ ?
266 ffmpeg is already organized in a highly modular manner and does not need to
267 be rewritten in a formal object language. Further, many of the developers
268 favor straight C; it works for them. For more arguments on this matter,
269 read "Programming Religion" at (@url{}).
271 @section Why are the ffmpeg programs devoid of debugging symbols ?
273 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
274 information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
275 you need the debug information, used the *_g versions.
277 @section I do not like the LGPL, can I contribute code under the GPL instead ?
279 Yes, as long as the code is optional and can easily and cleanly be placed
280 under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
281 or filter would be OK under GPL while a bugfix to LGPL code would not.
283 @section I want to compile xyz.c alone but my compiler produced many errors.
285 Common code is in its own files in libav* and is used by the individual
286 codecs. They will not work without the common parts, you have to compile
287 the whole libav*. If you wish, disable some parts with configure switches.
288 You can also try to hack it and remove more, but if you had problems fixing
289 the compilation failure then you are probably not qualified for this.
291 @section Visual C++ produces many errors.
293 Visual C++ is not compliant to the C standard and does not support
294 the inline assembly used in FFmpeg.
295 If you wish - for whatever weird reason - to use Visual C++ for your
296 project then you can link the Visual C++ code with libav* as long as
297 you compile the latter with a working C compiler. For more information, see
298 the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
300 There have been efforts to make FFmpeg compatible with Visual C++ in the
301 past. However, they have all been rejected as too intrusive, especially
302 since MinGW does the job perfectly adequately. None of the core developers
303 work with Visual C++ and thus this item is low priority. Should you find
304 the silver bullet that solves this problem, feel free to shoot it at us.
306 @section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat ?
308 You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
309 and libmpdemux/demux_lavf.c in MPlayer sources.
311 @section I get "No compatible shell script interpreter found." in MSys.
313 The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
315 @bye