[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 single pictures to movies?
21 First, rename your pictures to follow a numerical sequence.
22 For example, img1.jpg, img2.jpg, img3.jpg,...
23 Then you may run:
25 @example
26 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
27 @end example
29 Notice that @samp{%d} is replaced by the image number.
31 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
33 The same logic is used for any image format that ffmpeg reads.
35 @section How do I encode movie to single pictures?
37 Use:
39 @example
40 ffmpeg -i movie.mpg movie%d.jpg
41 @end example
43 The @file{movie.mpg} used as input will be converted to
44 @file{movie1.jpg}, @file{movie2.jpg}, etc...
46 Instead of relying on file format self-recognition, you may also use
47 @table @option
48 @item -vcodec ppm
49 @item -vcodec png
50 @item -vcodec mjpeg
51 @end table
52 to force the encoding.
54 Applying that to the previous example:
55 @example
56 ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
57 @end example
59 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
61 @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?
63 No. FFmpeg only supports open source codecs. Windows DLLs are not
64 portable, bloated and often slow.
66 @section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem?
68 This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work.
70 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
72 For multithreaded MPEG* encoding, the encoded slices must be independent,
73 otherwise thread n would practically have to wait for n-1 to finish, so it's
74 quite logical that there is a small reduction of quality. This is not a bug.
76 @section How can I read from the standard input or write to the standard output?
78 Use @file{-} as filename.
80 @section Why does ffmpeg not decode audio in VOB files?
82 The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
83 as the component that handles AC3 decoding (liba52) is currently released under
84 the GPL. If you have liba52 installed on your system, enable AC3 decoding
85 with @code{./configure --enable-liba52 --enable-gpl}. Take care: by
86 enabling AC3, you automatically change the license of libavcodec from
87 LGPL to GPL.
89 @section Which codecs are supported by Windows?
91 Windows does not support standard formats like MPEG very well, unless you
92 install some additional codecs
94 The following list of video codecs should work on most Windows systems:
95 @table @option
96 @item msmpeg4v2
97 .avi/.asf
98 @item msmpeg4
99 .asf only
100 @item wmv1
101 .asf only
102 @item wmv2
103 .asf only
104 @item mpeg4
105 only if you have some MPEG-4 codec installed like ffdshow or XviD
106 @item mpeg1
107 .mpg only
108 @end table
109 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
110 be mentioned that Microsoft claims a patent on the ASF format, and may sue
111 or threaten users who create ASF files with non-Microsoft software. It is
112 strongly advised to avoid ASF where possible.
114 The following list of audio codecs should work on most Windows systems:
115 @table @option
116 @item adpcm_ima_wav
117 @item adpcm_ms
118 @item pcm
119 @item mp3
120 if some MP3 codec like LAME is installed
121 @end table
123 @section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
125 This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
126 (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-420-2.4.26.patch?view=co}). This may also
127 apply cleanly to other 2.4-series kernels.
129 @section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
131 Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
132 will cause somewhat too strong filtering. A fix is to apply (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.4.26.patch?view=co})
133 or (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co})
134 and pass 'combfilter=2'.
136 @section I have a problem with an old version of ffmpeg; where should I report it?
137 Nowhere. Upgrade to the latest release or if there is no recent release upgrade
138 to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
139 become the first person in history to get an answer different from "upgrade
140 to Subversion HEAD".
142 @section -f jpeg doesn't work.
144 Try '-f image2 test%d.jpg'.
146 @section Why can I not change the framerate?
148 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
149 Choose a different codec with the -vcodec command line option.
151 @section ffmpeg does not work; What is wrong?
153 Try a 'make distclean' in the ffmpeg source directory before the build. If this does not help see
154 (@url{http://ffmpeg.org/bugreports.php}).
156 @section How do I encode XviD or DivX video with ffmpeg?
158 Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
159 standard (note that there are many other coding formats that use this
160 same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
161 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
162 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
163 force the fourcc 'xvid' to be stored as the video fourcc rather than the
164 default.
166 @section How do I encode videos which play on the iPod?
168 @table @option
169 @item needed stuff
170 -acodec libfaac -vcodec mpeg4 width<=320 height<=240
171 @item working stuff
172 4mv, title
173 @item non-working stuff
174 B-frames
175 @item example command line
176 ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 320x180 -title X output.mp4
177 @end table
179 @section How do I encode videos which play on the PSP?
181 @table @option
182 @item needed stuff
183 -acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
184 @item working stuff
185 4mv, title
186 @item non-working stuff
187 B-frames
188 @item example command line
189 ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -ar 24000 -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp output.mp4
190 @item needed stuff for H.264
191 -acodec libfaac -vcodec h264 width*height<=76800 width%16=0? height%16=0? -ar 48000 -coder 1 -r 30000/1001 or 15000/1001 -f psp
192 @item working stuff for H.264
193 title, loop filter
194 @item non-working stuff for H.264
196 @item example command line
197 ffmpeg -i input -acodec libfaac -ab 128kb -vcodec h264 -b 1200kb -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
198 @end table
200 @section Which are good parameters for encoding high quality MPEG-4?
202 '-mbd rd -flags +4mv+trell+aic -cmp 2 -subcmp 2 -g 300 -pass 1/2',
203 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
205 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
207 '-mbd rd -flags +trell -cmp 2 -subcmp 2 -g 100 -pass 1/2'
208 but beware the '-g 100' might cause problems with some decoders.
209 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
211 @section Interlaced video looks very bad when encoded with ffmpeg, whats wrong?
213 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
214 material, and try '-top 0/1' if the result looks really messed-up.
216 @section How can I read DirectShow files?
218 If you have built FFmpeg with @code{./configure --enable-avisynth}
219 (only possible on MinGW/Cygwin platforms),
220 then you may use any file that DirectShow can read as input.
221 (Be aware that this feature has been recently added,
222 so you will need to help yourself in case of problems.)
224 Just create an "input.avs" text file with this single line ...
225 @example
226 DirectShowSource("C:\path to your file\yourfile.asf")
227 @end example
228 ... and then feed that text file to FFmpeg:
229 @example
230 ffmpeg -i input.avs
231 @end example
233 For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
235 @section My bugreport/mail to ffmpeg-devel/user has not received any replies.
237 Likely reasons
238 @itemize
239 @item We are busy and haven't had time yet to read your report or
240 investigate the issue.
241 @item You didn't follow bugreports.html.
242 @item You didn't use Subversion HEAD.
243 @item You reported a segmentation fault without gdb output.
244 @item You describe a problem but not how to reproduce it.
245 @item It's unclear if you use ffmpeg as command line tool or use
246 libav* from another application.
247 @item You speak about a video having problems on playback but
248 not what you use to play it.
249 @item We have no faint clue what you are talking about besides
250 that it is related to FFmpeg.
251 @end itemize
253 @section How can I join video files?
255 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
256 merely concatenating them.
258 Hence you may concatenate your multimedia files by first transcoding them to
259 these privileged formats, then using the humble @code{cat} command (or the
260 equally humble @code{copy} under Windows), and finally transcoding back to your
261 format of choice.
263 @example
264 ffmpeg -i input1.avi -sameq intermediate1.mpg
265 ffmpeg -i input2.avi -sameq intermediate2.mpg
266 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
267 ffmpeg -i intermediate_all.mpg -sameq output.avi
268 @end example
270 Notice that you should either use @code{-sameq} or set a reasonably high
271 bitrate for your intermediate and output files, if you want to preserve
272 video quality.
274 Also notice that you may avoid the huge intermediate files by taking advantage
275 of named pipes, should your platform support it:
277 @example
278 mkfifo intermediate1.mpg
279 mkfifo intermediate2.mpg
280 ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null &
281 ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null &
282 cat intermediate1.mpg intermediate2.mpg |\
283 ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi
284 @end example
286 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
287 allow concatenation, and the transcoding step is almost lossless.
289 For example, let's say we want to join two FLV files into an output.flv file:
291 @example
292 mkfifo temp1.a
293 mkfifo temp1.v
294 mkfifo temp2.a
295 mkfifo temp2.v
296 mkfifo all.a
297 mkfifo all.v
298 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
299 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
300 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
301 ffmpeg -i input2.flv -an -f yuv4mpegpipe - > temp2.v < /dev/null &
302 cat temp1.a temp2.a > all.a &
303 cat temp1.v temp2.v > all.v &
304 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
305 -f yuv4mpegpipe -i all.v \
306 -sameq -y output.flv
307 rm temp[12].[av] all.[av]
308 @end example
310 @chapter Development
312 @section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
314 Like most open source projects FFmpeg suffers from a certain lack of
315 manpower. For this reason the developers have to prioritize the work
316 they do and putting out releases is not at the top of the list, fixing
317 bugs and reviewing patches takes precedence. Please don't complain or
318 request more timely and/or frequent releases unless you are willing to
319 help out creating them.
321 @section Why doesn't FFmpeg support feature [xyz]?
323 Because no one has taken on that task yet. FFmpeg development is
324 driven by the tasks that are important to the individual developers.
325 If there is a feature that is important to you, the best way to get
326 it implemented is to undertake the task yourself.
329 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
331 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
332 examine the source code for one of the many open source projects that
333 already incorporate ffmpeg at (@url{projects.php}).
335 @section Can you support my C compiler XXX?
337 It depends. If your compiler is C99-compliant, then patches to support
338 it are likely to be welcome if they do not pollute the source code
339 with @code{#ifdef}s related to the compiler.
341 @section Visual C++ produces many errors.
343 Visual C++ is not compliant to the C standard and does not support
344 the inline assembly used in FFmpeg.
345 If you wish - for whatever weird reason - to use Visual C++ for your
346 project then you can link the Visual C++ code with libav* as long as
347 you compile the latter with a working C compiler. For more information, see
348 the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
350 There have been efforts to make FFmpeg compatible with Visual C++ in the
351 past. However, they have all been rejected as too intrusive, especially
352 since MinGW does the job perfectly adequately. None of the core developers
353 work with Visual C++ and thus this item is low priority. Should you find
354 the silver bullet that solves this problem, feel free to shoot it at us.
356 @section Can I use FFmpeg or libavcodec under Windows?
358 Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
359 can link the resulting DLLs with any other Windows program. Read the
360 @emph{Native Windows Compilation} and @emph{Visual C++ compatibility}
361 sections in the FFmpeg documentation to find more information.
363 To get help and instructions for using FFmpeg under Windows, check out
364 the FFmpeg Windows Help Forum at
365 @url{http://arrozcru.no-ip.org/ffmpeg/}.
367 @section Can you add automake, libtool or autoconf support?
369 No. These tools are too bloated and they complicate the build.
371 @section Why not rewrite ffmpeg in object-oriented C++?
373 ffmpeg is already organized in a highly modular manner and does not need to
374 be rewritten in a formal object language. Further, many of the developers
375 favor straight C; it works for them. For more arguments on this matter,
376 read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
378 @section Why are the ffmpeg programs devoid of debugging symbols?
380 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
381 information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
382 you need the debug information, used the *_g versions.
384 @section I do not like the LGPL, can I contribute code under the GPL instead?
386 Yes, as long as the code is optional and can easily and cleanly be placed
387 under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
388 or filter would be OK under GPL while a bugfix to LGPL code would not.
390 @section I want to compile xyz.c alone but my compiler produced many errors.
392 Common code is in its own files in libav* and is used by the individual
393 codecs. They will not work without the common parts, you have to compile
394 the whole libav*. If you wish, disable some parts with configure switches.
395 You can also try to hack it and remove more, but if you had problems fixing
396 the compilation failure then you are probably not qualified for this.
398 @section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat?
400 You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
401 and libmpdemux/demux_lavf.c in MPlayer sources.
403 @section I get "No compatible shell script interpreter found." in MSys.
405 The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
407 @section I tried to pass RTP packets into a decoder, but it doesn't work.
409 RTP is a container format like any other, you must first depacketize the
410 codec frames/samples stored in RTP and then feed to the decoder.
412 @section Where can I find libav* headers for Pascal/Delphi?
414 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
416 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
418 see @url{http://svn.mplayerhq.hu/michael/trunk/docs/}
420 @section how do I feed H.263-RTP (and other codecs in rtp) to libavcodec?
422 Even if peculiar since it is network oriented, RTP is a container like any
423 other. You have to DEMUX RTP before feeding the payload to libavcodec.
424 In this specific case please look at rfc 4629 to see how it should be done.
426 @bye