1 \input texinfo @c -*- texinfo -*-
5 @center @titlefont{FFmpeg FAQ}
12 @chapter General Questions
14 @section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
16 Like most open source projects FFmpeg suffers from a certain lack of
17 manpower. For this reason the developers have to prioritize the work
18 they do and putting out releases is not at the top of the list, fixing
19 bugs and reviewing patches takes precedence. Please don't complain or
20 request more timely and/or frequent releases unless you are willing to
21 help out creating them.
23 @section I have a problem with an old version of FFmpeg; where should I report it?
24 Nowhere. We do not support old FFmpeg versions in any way, we simply lack
25 the time, motivation and manpower to do so. If you have a problem with an
26 old version of FFmpeg, upgrade to the latest git snapshot. If you
27 still experience the problem, then you can report it according to the
28 guidelines in @url{http://ffmpeg.org/bugreports.html}.
30 @section Why doesn't FFmpeg support feature [xyz]?
32 Because no one has taken on that task yet. FFmpeg development is
33 driven by the tasks that are important to the individual developers.
34 If there is a feature that is important to you, the best way to get
35 it implemented is to undertake the task yourself or sponsor a developer.
37 @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?
39 No. Windows DLLs are not portable, bloated and often slow.
40 Moreover FFmpeg strives to support all codecs natively.
41 A DLL loader is not conducive to that goal.
43 @section My bug report/mail to ffmpeg-devel/user has not received any replies.
47 @item We are busy and haven't had time yet to read your report or
48 investigate the issue.
49 @item You didn't follow @url{http://ffmpeg.org/bugreports.html}.
50 @item You didn't use git master.
51 @item You reported a segmentation fault without gdb output.
52 @item You describe a problem but not how to reproduce it.
53 @item It's unclear if you use ffmpeg as command line tool or use
54 libav* from another application.
55 @item You speak about a video having problems on playback but
56 not what you use to play it.
57 @item We have no faint clue what you are talking about besides
58 that it is related to FFmpeg.
61 @section Is there a forum for FFmpeg? I do not like mailing lists.
63 You may view our mailing lists with a more forum-alike look here:
64 @url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user},
65 but, if you post, please remember that our mailing list rules still apply there.
67 @section I cannot read this file although this format seems to be supported by ffmpeg.
69 Even if ffmpeg can read the container format, it may not support all its
70 codecs. Please consult the supported codec list in the ffmpeg
73 @section Which codecs are supported by Windows?
75 Windows does not support standard formats like MPEG very well, unless you
76 install some additional codecs.
78 The following list of video codecs should work on most Windows systems:
89 Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
93 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
94 be mentioned that Microsoft claims a patent on the ASF format, and may sue
95 or threaten users who create ASF files with non-Microsoft software. It is
96 strongly advised to avoid ASF where possible.
98 The following list of audio codecs should work on most Windows systems:
105 If some MP3 codec like LAME is installed.
111 @section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}
113 This is a bug in gcc. Do not report it to us. Instead, please report it to
114 the gcc developers. Note that we will not add workarounds for gcc bugs.
116 Also note that (some of) the gcc developers believe this is not a bug or
117 not a bug they should fix:
118 @url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}.
119 Then again, some of them do not know the difference between an undecidable
120 problem and an NP-hard problem...
124 @section ffmpeg does not work; what is wrong?
126 Try a @code{make distclean} in the ffmpeg source directory before the build.
127 If this does not help see
128 (@url{http://ffmpeg.org/bugreports.html}).
130 @section How do I encode single pictures into movies?
132 First, rename your pictures to follow a numerical sequence.
133 For example, img1.jpg, img2.jpg, img3.jpg,...
137 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
140 Notice that @samp{%d} is replaced by the image number.
142 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
144 If you have large number of pictures to rename, you can use the
145 following command to ease the burden. The command, using the bourne
146 shell syntax, symbolically links all files in the current directory
147 that match @code{*jpg} to the @file{/tmp} directory in the sequence of
148 @file{img001.jpg}, @file{img002.jpg} and so on.
151 x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
154 If you want to sequence them by oldest modified first, substitute
155 @code{$(ls -r -t *jpg)} in place of @code{*jpg}.
160 ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
163 The same logic is used for any image format that ffmpeg reads.
165 @section How do I encode movie to single pictures?
170 ffmpeg -i movie.mpg movie%d.jpg
173 The @file{movie.mpg} used as input will be converted to
174 @file{movie1.jpg}, @file{movie2.jpg}, etc...
176 Instead of relying on file format self-recognition, you may also use
182 to force the encoding.
184 Applying that to the previous example:
186 ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
189 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
191 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
193 For multithreaded MPEG* encoding, the encoded slices must be independent,
194 otherwise thread n would practically have to wait for n-1 to finish, so it's
195 quite logical that there is a small reduction of quality. This is not a bug.
197 @section How can I read from the standard input or write to the standard output?
199 Use @file{-} as file name.
201 @section -f jpeg doesn't work.
203 Try '-f image2 test%d.jpg'.
205 @section Why can I not change the framerate?
207 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
208 Choose a different codec with the -vcodec command line option.
210 @section How do I encode Xvid or DivX video with ffmpeg?
212 Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
213 standard (note that there are many other coding formats that use this
214 same standard). Thus, use '-vcodec mpeg4' to encode in these formats. The
215 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
216 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
217 force the fourcc 'xvid' to be stored as the video fourcc rather than the
220 @section How do I encode videos which play on the iPod?
224 -acodec libfaac -vcodec mpeg4 width<=320 height<=240
227 @item non-working stuff
229 @item example command line
230 ffmpeg -i input -acodec libfaac -ab 128k -vcodec mpeg4 -b 1200k -mbd 2 -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -s 320x180 -metadata title=X output.mp4
233 @section How do I encode videos which play on the PSP?
237 -acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
240 @item non-working stuff
242 @item example command line
243 ffmpeg -i input -acodec libfaac -ab 128k -vcodec mpeg4 -b 1200k -ar 24000 -mbd 2 -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -metadata title=X -f psp output.mp4
244 @item needed stuff for H.264
245 -acodec libfaac -vcodec libx264 width*height<=76800 width%16=0? height%16=0? -ar 48000 -coder 1 -r 30000/1001 or 15000/1001 -f psp
246 @item working stuff for H.264
248 @item non-working stuff for H.264
250 @item example command line
251 ffmpeg -i input -acodec libfaac -ab 128k -vcodec libx264 -b 1200k -ar 48000 -mbd 2 -coder 1 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -metadata title=X -f psp -flags loop -trellis 2 -partitions parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 output.mp4
252 @item higher resolution for newer PSP firmwares, width<=480, height<=272
253 -vcodec libx264 -level 21 -coder 1 -f psp
254 @item example command line
255 ffmpeg -i input -acodec libfaac -ab 128k -ac 2 -ar 48000 -vcodec libx264 -level 21 -b 640k -coder 1 -f psp -flags +loop -trellis 2 -partitions +parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 -g 250 -s 480x272 output.mp4
258 @section Which are good parameters for encoding high quality MPEG-4?
260 '-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2',
261 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
263 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
265 '-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2'
266 but beware the '-g 100' might cause problems with some decoders.
267 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
269 @section Interlaced video looks very bad when encoded with ffmpeg, what is wrong?
271 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
272 material, and try '-top 0/1' if the result looks really messed-up.
274 @section How can I read DirectShow files?
276 If you have built FFmpeg with @code{./configure --enable-avisynth}
277 (only possible on MinGW/Cygwin platforms),
278 then you may use any file that DirectShow can read as input.
280 Just create an "input.avs" text file with this single line ...
282 DirectShowSource("C:\path to your file\yourfile.asf")
284 ... and then feed that text file to ffmpeg:
289 For ANY other help on Avisynth, please visit the
290 @uref{http://www.avisynth.org/, Avisynth homepage}.
292 @section How can I join video files?
294 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
295 merely concatenating them.
297 Hence you may concatenate your multimedia files by first transcoding them to
298 these privileged formats, then using the humble @code{cat} command (or the
299 equally humble @code{copy} under Windows), and finally transcoding back to your
303 ffmpeg -i input1.avi -sameq intermediate1.mpg
304 ffmpeg -i input2.avi -sameq intermediate2.mpg
305 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
306 ffmpeg -i intermediate_all.mpg -sameq output.avi
309 Notice that you should either use @code{-sameq} or set a reasonably high
310 bitrate for your intermediate and output files, if you want to preserve
313 Also notice that you may avoid the huge intermediate files by taking advantage
314 of named pipes, should your platform support it:
317 mkfifo intermediate1.mpg
318 mkfifo intermediate2.mpg
319 ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null &
320 ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null &
321 cat intermediate1.mpg intermediate2.mpg |\
322 ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi
325 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
326 allow concatenation, and the transcoding step is almost lossless.
327 When using multiple yuv4mpegpipe(s), the first line needs to be discarded
328 from all but the first stream. This can be accomplished by piping through
329 @code{tail} as seen below. Note that when piping through @code{tail} you
330 must use command grouping, @code{@{ ;@}}, to background properly.
332 For example, let's say we want to join two FLV files into an output.flv file:
341 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
342 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
343 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
344 @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
345 cat temp1.a temp2.a > all.a &
346 cat temp1.v temp2.v > all.v &
347 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
348 -f yuv4mpegpipe -i all.v \
350 rm temp[12].[av] all.[av]
353 @section The ffmpeg program does not respect the -maxrate setting, some frames are bigger than maxrate/fps.
355 Read the MPEG spec about video buffer verifier.
357 @section I want CBR, but no matter what I do frame sizes differ.
359 You do not understand what CBR is, please read the MPEG spec.
360 Read about video buffer verifier and constant bitrate.
361 The one sentence summary is that there is a buffer and the input rate is
362 constant, the output can vary as needed.
364 @section How do I check if a stream is CBR?
366 To quote the MPEG-2 spec:
367 "There is no way to tell that a bitstream is constant bitrate without
368 examining all of the vbv_delay values and making complicated computations."
373 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
375 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
376 examine the source code for one of the many open source projects that
377 already incorporate FFmpeg at (@url{projects.html}).
379 @section Can you support my C compiler XXX?
381 It depends. If your compiler is C99-compliant, then patches to support
382 it are likely to be welcome if they do not pollute the source code
383 with @code{#ifdef}s related to the compiler.
385 @section Is Microsoft Visual C++ supported?
387 No. Microsoft Visual C++ is not compliant to the C99 standard and does
388 not - among other things - support the inline assembly used in FFmpeg.
389 If you wish to use MSVC++ for your
390 project then you can link the MSVC++ code with libav* as long as
391 you compile the latter with a working C compiler. For more information, see
392 the @emph{Microsoft Visual C++ compatibility} section in the FFmpeg
395 There have been efforts to make FFmpeg compatible with MSVC++ in the
396 past. However, they have all been rejected as too intrusive, especially
397 since MinGW does the job adequately. None of the core developers
398 work with MSVC++ and thus this item is low priority. Should you find
399 the silver bullet that solves this problem, feel free to shoot it at us.
401 We strongly recommend you to move over from MSVC++ to MinGW tools.
403 @section Can I use FFmpeg or libavcodec under Windows?
405 Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg.
406 Read the @emph{Windows} section in the FFmpeg documentation to find more
409 To get help and instructions for building FFmpeg under Windows, check out
410 the FFmpeg Windows Help Forum at
411 @url{http://ffmpeg.arrozcru.org/}.
413 @section Can you add automake, libtool or autoconf support?
415 No. These tools are too bloated and they complicate the build.
417 @section Why not rewrite ffmpeg in object-oriented C++?
419 FFmpeg is already organized in a highly modular manner and does not need to
420 be rewritten in a formal object language. Further, many of the developers
421 favor straight C; it works for them. For more arguments on this matter,
422 read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
424 @section Why are the ffmpeg programs devoid of debugging symbols?
426 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
427 information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
428 you need the debug information, use the *_g versions.
430 @section I do not like the LGPL, can I contribute code under the GPL instead?
432 Yes, as long as the code is optional and can easily and cleanly be placed
433 under #if CONFIG_GPL without breaking anything. So for example a new codec
434 or filter would be OK under GPL while a bug fix to LGPL code would not.
436 @section I want to compile xyz.c alone but my compiler produced many errors.
438 Common code is in its own files in libav* and is used by the individual
439 codecs. They will not work without the common parts, you have to compile
440 the whole libav*. If you wish, disable some parts with configure switches.
441 You can also try to hack it and remove more, but if you had problems fixing
442 the compilation failure then you are probably not qualified for this.
444 @section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available.
446 FFmpeg is a pure C project, so to use the libraries within your C++ application
447 you need to explicitly state that you are using a C library. You can do this by
448 encompassing your FFmpeg includes using @code{extern "C"}.
450 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
452 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
454 You have to implement a URLProtocol, see @file{libavformat/file.c} in
455 FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer sources.
457 @section I get "No compatible shell script interpreter found." in MSys.
459 The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
461 @section I get "./configure: line <xxx>: pr: command not found" in MSys.
463 The standard MSys install doesn't come with pr. You need to get it from the coreutils package.
465 @section Where can I find libav* headers for Pascal/Delphi?
467 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
469 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
471 see @url{http://www.ffmpeg.org/~michael/}
473 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
475 Even if peculiar since it is network oriented, RTP is a container like any
476 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
477 In this specific case please look at RFC 4629 to see how it should be done.
479 @section AVStream.r_frame_rate is wrong, it is much larger than the framerate.
481 r_frame_rate is NOT the average framerate, it is the smallest framerate
482 that can accurately represent all timestamps. So no, it is not
483 wrong if it is larger than the average!
484 For example, if you have mixed 25 and 30 fps content, then r_frame_rate