1 \input texinfo @c -*- texinfo -*-
6 @center @titlefont{FFmpeg FAQ}
11 @chapter General Questions
13 @section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
15 Like most open source projects FFmpeg suffers from a certain lack of
16 manpower. For this reason the developers have to prioritize the work
17 they do and putting out releases is not at the top of the list, fixing
18 bugs and reviewing patches takes precedence. Please don't complain or
19 request more timely and/or frequent releases unless you are willing to
20 help out creating them.
22 @section I have a problem with an old version of FFmpeg; where should I report it?
23 Nowhere. Upgrade to the latest release or if there is no recent release upgrade
24 to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
25 become the first person in history to get an answer different from "upgrade
28 @section Why doesn't FFmpeg support feature [xyz]?
30 Because no one has taken on that task yet. FFmpeg development is
31 driven by the tasks that are important to the individual developers.
32 If there is a feature that is important to you, the best way to get
33 it implemented is to undertake the task yourself or sponsor a developer.
35 @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?
37 No. Windows DLLs are not portable, bloated and often slow.
38 Moreover FFmpeg strives to support all codecs natively.
39 A DLL loader is not conducive to that goal.
41 @section My bugreport/mail to ffmpeg-devel/user has not received any replies.
45 @item We are busy and haven't had time yet to read your report or
46 investigate the issue.
47 @item You didn't follow bugreports.html.
48 @item You didn't use Subversion HEAD.
49 @item You reported a segmentation fault without gdb output.
50 @item You describe a problem but not how to reproduce it.
51 @item It's unclear if you use ffmpeg as command line tool or use
52 libav* from another application.
53 @item You speak about a video having problems on playback but
54 not what you use to play it.
55 @item We have no faint clue what you are talking about besides
56 that it is related to FFmpeg.
59 @section Is there a forum for FFmpeg? I do not like mailing lists.
61 Yes, (@url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user}).
63 @section I cannot read this file although this format seems to be supported by ffmpeg.
65 Even if ffmpeg can read the container format, it may not support all its
66 codecs. Please consult the supported codec list in the ffmpeg
69 @section Which codecs are supported by Windows?
71 Windows does not support standard formats like MPEG very well, unless you
72 install some additional codecs
74 The following list of video codecs should work on most Windows systems:
85 only if you have some MPEG-4 codec installed like ffdshow or XviD
89 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
90 be mentioned that Microsoft claims a patent on the ASF format, and may sue
91 or threaten users who create ASF files with non-Microsoft software. It is
92 strongly advised to avoid ASF where possible.
94 The following list of audio codecs should work on most Windows systems:
100 if some MP3 codec like LAME is installed
106 @section ffmpeg does not work; What is wrong?
108 Try a @code{make distclean} in the ffmpeg source directory before the build. If this does not help see
109 (@url{http://ffmpeg.org/bugreports.html}).
111 @section How do I encode single pictures to movies?
113 First, rename your pictures to follow a numerical sequence.
114 For example, img1.jpg, img2.jpg, img3.jpg,...
118 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
121 Notice that @samp{%d} is replaced by the image number.
123 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
125 The same logic is used for any image format that ffmpeg reads.
127 @section How do I encode movie to single pictures?
132 ffmpeg -i movie.mpg movie%d.jpg
135 The @file{movie.mpg} used as input will be converted to
136 @file{movie1.jpg}, @file{movie2.jpg}, etc...
138 Instead of relying on file format self-recognition, you may also use
144 to force the encoding.
146 Applying that to the previous example:
148 ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
151 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
153 @section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem?
155 This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work.
157 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
159 For multithreaded MPEG* encoding, the encoded slices must be independent,
160 otherwise thread n would practically have to wait for n-1 to finish, so it's
161 quite logical that there is a small reduction of quality. This is not a bug.
163 @section How can I read from the standard input or write to the standard output?
165 Use @file{-} as filename.
167 @section Why does FFmpeg not decode audio in VOB files?
169 The audio is AC-3 (a.k.a. A/52). AC-3 decoding is an optional component in FFmpeg
170 as the component that handles AC-3 decoding is currently released under the GPL.
171 Enable AC-3 decoding with @code{./configure --enable-gpl}. Take care: By
172 enabling AC-3, you automatically change the license of libavcodec from
175 @section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
177 This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
178 (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-420-2.4.26.patch?view=co}). This may also
179 apply cleanly to other 2.4-series kernels.
181 @section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
183 Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
184 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})
185 or (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co})
186 and pass 'combfilter=2'.
188 @section -f jpeg doesn't work.
190 Try '-f image2 test%d.jpg'.
192 @section Why can I not change the framerate?
194 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
195 Choose a different codec with the -vcodec command line option.
197 @section How do I encode XviD or DivX video with ffmpeg?
199 Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
200 standard (note that there are many other coding formats that use this
201 same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
202 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
203 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
204 force the fourcc 'xvid' to be stored as the video fourcc rather than the
207 @section How do I encode videos which play on the iPod?
211 -acodec libfaac -vcodec mpeg4 width<=320 height<=240
214 @item non-working stuff
216 @item example command line
217 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
220 @section How do I encode videos which play on the PSP?
224 -acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
227 @item non-working stuff
229 @item example command line
230 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
231 @item needed stuff for H.264
232 -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
233 @item working stuff for H.264
235 @item non-working stuff for H.264
237 @item example command line
238 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
241 @section Which are good parameters for encoding high quality MPEG-4?
243 '-mbd rd -flags +4mv+trell+aic -cmp 2 -subcmp 2 -g 300 -pass 1/2',
244 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
246 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
248 '-mbd rd -flags +trell -cmp 2 -subcmp 2 -g 100 -pass 1/2'
249 but beware the '-g 100' might cause problems with some decoders.
250 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
252 @section Interlaced video looks very bad when encoded with ffmpeg, whats wrong?
254 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
255 material, and try '-top 0/1' if the result looks really messed-up.
257 @section How can I read DirectShow files?
259 If you have built FFmpeg with @code{./configure --enable-avisynth}
260 (only possible on MinGW/Cygwin platforms),
261 then you may use any file that DirectShow can read as input.
262 (Be aware that this feature has been recently added,
263 so you will need to help yourself in case of problems.)
265 Just create an "input.avs" text file with this single line ...
267 DirectShowSource("C:\path to your file\yourfile.asf")
269 ... and then feed that text file to FFmpeg:
274 For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
276 @section How can I join video files?
278 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
279 merely concatenating them.
281 Hence you may concatenate your multimedia files by first transcoding them to
282 these privileged formats, then using the humble @code{cat} command (or the
283 equally humble @code{copy} under Windows), and finally transcoding back to your
287 ffmpeg -i input1.avi -sameq intermediate1.mpg
288 ffmpeg -i input2.avi -sameq intermediate2.mpg
289 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
290 ffmpeg -i intermediate_all.mpg -sameq output.avi
293 Notice that you should either use @code{-sameq} or set a reasonably high
294 bitrate for your intermediate and output files, if you want to preserve
297 Also notice that you may avoid the huge intermediate files by taking advantage
298 of named pipes, should your platform support it:
301 mkfifo intermediate1.mpg
302 mkfifo intermediate2.mpg
303 ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null &
304 ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null &
305 cat intermediate1.mpg intermediate2.mpg |\
306 ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi
309 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
310 allow concatenation, and the transcoding step is almost lossless.
312 For example, let's say we want to join two FLV files into an output.flv file:
321 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
322 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
323 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
324 ffmpeg -i input2.flv -an -f yuv4mpegpipe - > temp2.v < /dev/null &
325 cat temp1.a temp2.a > all.a &
326 cat temp1.v temp2.v > all.v &
327 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
328 -f yuv4mpegpipe -i all.v \
330 rm temp[12].[av] all.[av]
333 @section FFmpeg does not adhere to the -maxrate setting, some frames are bigger than maxrate/fps.
335 Read the MPEG spec about video buffer verifier.
337 @section I want CBR, but no matter what I do frame sizes differ.
339 You do not understand what CBR is, please read the MPEG spec.
340 Read about video buffer verifier and constant bitrate.
341 The one sentence summary is that there is a buffer and the input rate is
342 constant, the output can vary as needed.
344 @section How do I check if a stream is CBR?
346 To quote the MPEG-2 spec:
347 "There is no way to tell that a bitstream is constant bitrate without
348 examining all of the vbv_delay values and making complicated computations."
353 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
355 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
356 examine the source code for one of the many open source projects that
357 already incorporate ffmpeg at (@url{projects.html}).
359 @section Can you support my C compiler XXX?
361 It depends. If your compiler is C99-compliant, then patches to support
362 it are likely to be welcome if they do not pollute the source code
363 with @code{#ifdef}s related to the compiler.
365 @section Is Microsoft Visual C++ supported?
367 No. Microsoft Visual C++ is not compliant to the C99 standard and does
368 not - among other things - support the inline assembly used in FFmpeg.
369 If you wish to use MSVC++ for your
370 project then you can link the MSVC++ code with libav* as long as
371 you compile the latter with a working C compiler. For more information, see
372 the @emph{Microsoft Visual C++ compatibility} section in the FFmpeg
375 There have been efforts to make FFmpeg compatible with MSVC++ in the
376 past. However, they have all been rejected as too intrusive, especially
377 since MinGW does the job adequately. None of the core developers
378 work with MSVC++ and thus this item is low priority. Should you find
379 the silver bullet that solves this problem, feel free to shoot it at us.
381 We strongly recommend you to move over from MSVC++ to MinGW tools.
383 @section Can I use FFmpeg or libavcodec under Windows?
385 Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg.
386 Read the @emph{Windows} section in the FFmpeg documentation to find more
389 To get help and instructions for building FFmpeg under Windows, check out
390 the FFmpeg Windows Help Forum at
391 @url{http://arrozcru.no-ip.org/ffmpeg/}.
393 @section Can you add automake, libtool or autoconf support?
395 No. These tools are too bloated and they complicate the build.
397 @section Why not rewrite ffmpeg in object-oriented C++?
399 ffmpeg is already organized in a highly modular manner and does not need to
400 be rewritten in a formal object language. Further, many of the developers
401 favor straight C; it works for them. For more arguments on this matter,
402 read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
404 @section Why are the ffmpeg programs devoid of debugging symbols?
406 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
407 information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
408 you need the debug information, used the *_g versions.
410 @section I do not like the LGPL, can I contribute code under the GPL instead?
412 Yes, as long as the code is optional and can easily and cleanly be placed
413 under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
414 or filter would be OK under GPL while a bugfix to LGPL code would not.
416 @section I want to compile xyz.c alone but my compiler produced many errors.
418 Common code is in its own files in libav* and is used by the individual
419 codecs. They will not work without the common parts, you have to compile
420 the whole libav*. If you wish, disable some parts with configure switches.
421 You can also try to hack it and remove more, but if you had problems fixing
422 the compilation failure then you are probably not qualified for this.
424 @section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available.
426 FFmpeg is a pure C project, so to use the libraries within your C++ application
427 you need to explicitly state that you are using a C library. You can do this by
428 encompassing your FFmpeg includes using @code{extern "C"}.
430 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
432 @section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat?
434 You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
435 and libmpdemux/demux_lavf.c in MPlayer sources.
437 @section I get "No compatible shell script interpreter found." in MSys.
439 The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
441 @section I get "./configure: line <xxx>: pr: command not found" in MSys.
443 The standard MSys install doesn't come with pr. You need to get it from the coreutils package.
445 @section I tried to pass RTP packets into a decoder, but it doesn't work.
447 RTP is a container format like any other, you must first depacketize the
448 codec frames/samples stored in RTP and then feed to the decoder.
450 @section Where can I find libav* headers for Pascal/Delphi?
452 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
454 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
456 see @url{http://svn.mplayerhq.hu/michael/trunk/docs/}
458 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
460 Even if peculiar since it is network oriented, RTP is a container like any
461 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
462 In this specific case please look at RFC 4629 to see how it should be done.
464 @section AVStream.r_frame_rate is wrong, it is much larger than the framerate.
466 r_frame_rate is NOT the average framerate, it is the smallest framerate
467 that can accurately represent all timestamps. So no, it is not
468 wrong if it is larger than the average!
469 For example, if you have mixed 25 and 30 fps content, then r_frame_rate