1 \input texinfo @c -*- texinfo -*-
6 @center @titlefont{FFmpeg FAQ}
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
19 @section How do I encode JPEGs to another format ?
21 If the JPEGs are named img1.jpg, img2.jpg, img3.jpg,..., use:
24 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
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.
42 ffmpeg -f image2 -i menu.png -f image2 menu.jpg
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
53 to force the encoding.
55 Applying that to the previous example:
57 ffmpeg -f image2 -vcodec png -i menu.png -f image2 -vcodec mjpeg menu.jpg
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 Why do I see a slight quality degradation with multithreaded MPEG* encoding ?
69 For multithreaded MPEG* encoding, the encoded slices must be independent,
70 otherwise thread n would practically have to wait for n-1 to finish, so it's
71 quite logical that there is a small reduction of quality. This is not a bug.
73 @section How can I read from the standard input or write to the standard output ?
75 Use @file{-} as filename.
77 @section Why does ffmpeg not decode audio in VOB files ?
79 The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
80 as the component that handles AC3 decoding (liba52) is currently released under
81 the GPL. If you have liba52 installed on your system, enable AC3 decoding
82 with @code{./configure --enable-a52}. Take care: by
83 enabling AC3, you automatically change the license of libavcodec from
86 @section Which codecs are supported by Windows ?
88 Windows does not support standard formats like MPEG very well, unless you
89 install some additional codecs
91 The following list of video codecs should work on most Windows systems:
102 only if you have some MPEG-4 codec installed like ffdshow or XviD
106 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
107 be mentioned that Microsoft claims a patent on the ASF format, and may sue
108 or threaten users who create ASF files with non-Microsoft software. It is
109 strongly advised to avoid ASF where possible.
111 The following list of audio codecs should work on most Windows systems:
117 if some MP3 codec like LAME is installed
120 @section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
122 This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
123 (@url{http://mplayerhq.hu/~michael/bttv-420-2.4.26.patch}). This may also
124 apply cleanly to other 2.4-series kernels.
126 @section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
128 Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
129 will cause somewhat too strong filtering. A fix is to apply (@url{http://mplayerhq.hu/~michael/bttv-comb-2.4.26.patch})
130 or (@url{http://mplayerhq.hu/~michael/bttv-comb-2.6.6.patch})
131 and pass 'combfilter=2'.
133 @section I have a problem with an old version of ffmpeg; where should I report it?
134 Nowhere. Upgrade to the latest release or if there is no recent release upgrade
135 to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
136 become the first person in history to get an answer different from "upgrade
139 @section -f jpeg doesn't work.
141 Try '-f image2 test%d.jpg'.
143 @section Why can I not change the framerate?
145 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
146 Choose a different codec with the -vcodec command line option.
148 @section ffmpeg does not work; What is wrong?
150 Try a 'make distclean' in the ffmpeg source directory. If this does not help see
151 (@url{http://ffmpeg.org/bugreports.php}).
153 @section How do I encode XviD or DivX video with ffmpeg?
155 Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
156 standard (note that there are many other coding formats that use this
157 same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
158 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
159 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
160 force the fourcc 'xvid' to be stored as the video fourcc rather than the
163 @section How do I encode videos which play on the iPod?
167 -acodec aac -vcodec mpeg4 width<=320 height<=240
170 @item non-working stuff
172 @item example command line
173 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
176 @section How do I encode videos which play on the PSP?
180 -acodec aac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
183 @item non-working stuff
185 @item example command line
186 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
187 @item needed stuff for H.264
188 -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
189 @item working stuff for H.264
191 @item non-working stuff for H.264
193 @item example command line
194 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
197 @section How can I read DirectShow files?
199 If you have built FFmpeg with @code{./configure --enable-avisynth}
200 (only possible on MinGW/Cygwin platforms),
201 then you may use any file that DirectShow can read as input.
202 (Be aware that this feature has been recently added,
203 so you will need to help yourself in case of problems.)
205 Just create an "input.avs" text file with this single line ...
207 DirectShowSource("C:\path to your file\yourfile.asf")
209 ... and then feed that text file to FFmpeg:
214 For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
218 @section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
220 Like most open source projects FFmpeg suffers from a certain lack of
221 manpower. For this reason the developers have to prioritize the work
222 they do and putting out releases is not at the top of the list, fixing
223 bugs and reviewing patches takes precedence. Please don't complain or
224 request more timely and/or frequent releases unless you are willing to
225 help out creating them.
227 @section Why doesn't FFmpeg support feature [xyz]?
229 Because no one has taken on that task yet. FFmpeg development is
230 driven by the tasks that are important to the individual developers.
231 If there is a feature that is important to you, the best way to get
232 it implemented is to undertake the task yourself.
235 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat ?
237 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
238 examine the source code for one of the many open source projects that
239 already incorporate ffmpeg at (@url{projects.php}).
241 @section Can you support my C compiler XXX ?
243 No. Only GCC is supported. GCC is ported to most systems available and there
244 is no need to pollute the source code with @code{#ifdef}s
245 related to the compiler.
247 @section Can I use FFmpeg or libavcodec under Windows ?
249 Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
250 can link the resulting DLLs with any other Windows program. Read the
251 @emph{Native Windows Compilation} and @emph{Visual C++ compatibility}
252 sections in the FFmpeg documentation to find more information.
254 @section Can you add automake, libtool or autoconf support ?
256 No. These tools are too bloated and they complicate the build. Moreover,
257 since only @samp{gcc} is supported they would add little advantages in
258 terms of portability.
260 @section Why not rewrite ffmpeg in object-oriented C++ ?
262 ffmpeg is already organized in a highly modular manner and does not need to
263 be rewritten in a formal object language. Further, many of the developers
264 favor straight C; it works for them. For more arguments on this matter,
265 read "Programming Religion" at (@url{http://lkml.org/faq/lkmlfaq-15.html}).
267 @section Why are the ffmpeg programs devoid of debugging symbols ?
269 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
270 information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
271 you need the debug information, used the *_g versions.
273 @section I do not like the LGPL, can I contribute code under the GPL instead ?
275 Yes, as long as the code is optional and can easily and cleanly be placed
276 under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
277 or filter would be OK under GPL while a bugfix to LGPL code would not.
279 @section I want to compile xyz.c alone but my compiler produced many errors.
281 Common code is in its own files in libav* and is used by the individual
282 codecs. They will not work without the common parts, you have to compile
283 the whole libav*. If you wish, disable some parts with configure switches.
284 You can also try to hack it and remove more, but if you had problems fixing
285 the compilation failure then you are probably not qualified for this.
287 @section Visual C++ produces many errors.
289 Visual C++ is not compliant to the C standard and does not support
290 the inline assembly used in FFmpeg.
291 If you wish - for whatever weird reason - to use Visual C++ for your
292 project then you can link the Visual C++ code with libav* as long as
293 you compile the latter with a working C compiler. For more information, see
294 the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
296 There have been efforts to make FFmpeg compatible with Visual C++ in the
297 past. However, they have all been rejected as too intrusive, especially
298 since MinGW does the job perfectly adequately. None of the core developers
299 work with Visual C++ and thus this item is low priority. Should you find
300 the silver bullet that solves this problem, feel free to shoot it at us.
302 @section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat ?
304 You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
305 and libmpdemux/demux_lavf.c in MPlayer sources.