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. We do not support old FFmpeg versions in any way, we simply lack
24 the time, motivation and manpower to do so. If you have a problem with an
25 old version of FFmpeg, upgrade to the latest Subversion snapshot. If you
26 still experience the problem, then you can report it according to the
27 guidelines in @url{http://ffmpeg.org/bugreports.html}.
29 @section Why doesn't FFmpeg support feature [xyz]?
31 Because no one has taken on that task yet. FFmpeg development is
32 driven by the tasks that are important to the individual developers.
33 If there is a feature that is important to you, the best way to get
34 it implemented is to undertake the task yourself or sponsor a developer.
36 @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?
38 No. Windows DLLs are not portable, bloated and often slow.
39 Moreover FFmpeg strives to support all codecs natively.
40 A DLL loader is not conducive to that goal.
42 @section My bug report/mail to ffmpeg-devel/user has not received any replies.
46 @item We are busy and haven't had time yet to read your report or
47 investigate the issue.
48 @item You didn't follow @url{http://ffmpeg.org/bugreports.html}.
49 @item You didn't use Subversion HEAD.
50 @item You reported a segmentation fault without gdb output.
51 @item You describe a problem but not how to reproduce it.
52 @item It's unclear if you use ffmpeg as command line tool or use
53 libav* from another application.
54 @item You speak about a video having problems on playback but
55 not what you use to play it.
56 @item We have no faint clue what you are talking about besides
57 that it is related to FFmpeg.
60 @section Is there a forum for FFmpeg? I do not like mailing lists.
62 You may view our mailing lists with a more forum-alike look here:
63 @url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user},
64 but, if you post, please remember that our mailing list rules still apply there.
66 @section I cannot read this file although this format seems to be supported by ffmpeg.
68 Even if ffmpeg can read the container format, it may not support all its
69 codecs. Please consult the supported codec list in the ffmpeg
72 @section Which codecs are supported by Windows?
74 Windows does not support standard formats like MPEG very well, unless you
75 install some additional codecs.
77 The following list of video codecs should work on most Windows systems:
88 Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
92 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
93 be mentioned that Microsoft claims a patent on the ASF format, and may sue
94 or threaten users who create ASF files with non-Microsoft software. It is
95 strongly advised to avoid ASF where possible.
97 The following list of audio codecs should work on most Windows systems:
104 If some MP3 codec like LAME is installed.
110 @section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}
112 This is a bug in gcc. Do not report it to us. Instead, please report it to
113 the gcc developers. Note that we will not add workarounds for gcc bugs.
115 Also note that (some of) the gcc developers believe this is not a bug or
116 not a bug they should fix:
117 @url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}.
118 Then again, some of them do not know the difference between an undecidable
119 problem and an NP-hard problem...
123 @section ffmpeg does not work; what is wrong?
125 Try a @code{make distclean} in the ffmpeg source directory before the build. If this does not help see
126 (@url{http://ffmpeg.org/bugreports.html}).
128 @section How do I encode single pictures into movies?
130 First, rename your pictures to follow a numerical sequence.
131 For example, img1.jpg, img2.jpg, img3.jpg,...
135 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
138 Notice that @samp{%d} is replaced by the image number.
140 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
142 If you have large number of pictures to rename, you can use the
143 following command to ease the burden. The command, using the bourne
144 shell syntax, symbolically links all files in the current directory
145 that match @code{*jpg} to the @file{/tmp} directory in the sequence of
146 @file{img001.jpg}, @file{img002.jpg} and so on.
149 x=1; for i in *jpg; do counter=$(printf %03d $x); ln "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
152 If you want to sequence them by oldest modified first, substitute
153 @code{$(ls -r -t *jpg)} in place of @code{*jpg}.
158 ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
161 The same logic is used for any image format that ffmpeg reads.
163 @section How do I encode movie to single pictures?
168 ffmpeg -i movie.mpg movie%d.jpg
171 The @file{movie.mpg} used as input will be converted to
172 @file{movie1.jpg}, @file{movie2.jpg}, etc...
174 Instead of relying on file format self-recognition, you may also use
180 to force the encoding.
182 Applying that to the previous example:
184 ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
187 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
189 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
191 For multithreaded MPEG* encoding, the encoded slices must be independent,
192 otherwise thread n would practically have to wait for n-1 to finish, so it's
193 quite logical that there is a small reduction of quality. This is not a bug.
195 @section How can I read from the standard input or write to the standard output?
197 Use @file{-} as file name.
199 @section -f jpeg doesn't work.
201 Try '-f image2 test%d.jpg'.
203 @section Why can I not change the framerate?
205 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
206 Choose a different codec with the -vcodec command line option.
208 @section How do I encode Xvid or DivX video with ffmpeg?
210 Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
211 standard (note that there are many other coding formats that use this
212 same standard). Thus, use '-vcodec mpeg4' to encode in these formats. The
213 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
214 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
215 force the fourcc 'xvid' to be stored as the video fourcc rather than the
218 @section How do I encode videos which play on the iPod?
222 -acodec libfaac -vcodec mpeg4 width<=320 height<=240
225 @item non-working stuff
227 @item example command line
228 ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -mbd 2 -flags +4mv -trellis 2 -aic 2 -cmp 2 -subcmp 2 -s 320x180 -metadata title=X output.mp4
231 @section How do I encode videos which play on the PSP?
235 -acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
238 @item non-working stuff
240 @item example command line
241 ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -ar 24000 -mbd 2 -flags +4mv -trellis 2 -aic 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -metadata title=X -f psp output.mp4
242 @item needed stuff for H.264
243 -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
244 @item working stuff for H.264
246 @item non-working stuff for H.264
248 @item example command line
249 ffmpeg -i input -acodec libfaac -ab 128kb -vcodec libx264 -b 1200kb -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
250 @item higher resolution for newer PSP firmwares, width<=480, height<=272
251 -vcodec libx264 -level 21 -coder 1 -f psp
252 @item example command line
253 ffmpeg -i input -acodec libfaac -ab 128kb -ac 2 -ar 48000 -vcodec libx264 -level 21 -b 640kb -coder 1 -f psp -flags +loop -trellis 2 -partitions +parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 -g 250 -s 480x272 output.mp4
256 @section Which are good parameters for encoding high quality MPEG-4?
258 '-mbd rd -flags +4mv+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2',
259 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
261 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
263 '-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2'
264 but beware the '-g 100' might cause problems with some decoders.
265 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
267 @section Interlaced video looks very bad when encoded with ffmpeg, what is wrong?
269 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
270 material, and try '-top 0/1' if the result looks really messed-up.
272 @section How can I read DirectShow files?
274 If you have built FFmpeg with @code{./configure --enable-avisynth}
275 (only possible on MinGW/Cygwin platforms),
276 then you may use any file that DirectShow can read as input.
278 Just create an "input.avs" text file with this single line ...
280 DirectShowSource("C:\path to your file\yourfile.asf")
282 ... and then feed that text file to FFmpeg:
287 For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
289 @section How can I join video files?
291 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
292 merely concatenating them.
294 Hence you may concatenate your multimedia files by first transcoding them to
295 these privileged formats, then using the humble @code{cat} command (or the
296 equally humble @code{copy} under Windows), and finally transcoding back to your
300 ffmpeg -i input1.avi -sameq intermediate1.mpg
301 ffmpeg -i input2.avi -sameq intermediate2.mpg
302 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
303 ffmpeg -i intermediate_all.mpg -sameq output.avi
306 Notice that you should either use @code{-sameq} or set a reasonably high
307 bitrate for your intermediate and output files, if you want to preserve
310 Also notice that you may avoid the huge intermediate files by taking advantage
311 of named pipes, should your platform support it:
314 mkfifo intermediate1.mpg
315 mkfifo intermediate2.mpg
316 ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null &
317 ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null &
318 cat intermediate1.mpg intermediate2.mpg |\
319 ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi
322 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
323 allow concatenation, and the transcoding step is almost lossless.
324 When using multiple yuv4mpegpipe(s), the first line needs to be discarded
325 from all but the first stream. This can be accomplished by piping through
326 @code{tail} as seen below. Note that when piping through @code{tail} you
327 must use command grouping, @code{@{ ;@}}, to background properly.
329 For example, let's say we want to join two FLV files into an output.flv file:
338 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
339 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
340 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
341 @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
342 cat temp1.a temp2.a > all.a &
343 cat temp1.v temp2.v > all.v &
344 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
345 -f yuv4mpegpipe -i all.v \
347 rm temp[12].[av] all.[av]
350 @section FFmpeg does not adhere to the -maxrate setting, some frames are bigger than maxrate/fps.
352 Read the MPEG spec about video buffer verifier.
354 @section I want CBR, but no matter what I do frame sizes differ.
356 You do not understand what CBR is, please read the MPEG spec.
357 Read about video buffer verifier and constant bitrate.
358 The one sentence summary is that there is a buffer and the input rate is
359 constant, the output can vary as needed.
361 @section How do I check if a stream is CBR?
363 To quote the MPEG-2 spec:
364 "There is no way to tell that a bitstream is constant bitrate without
365 examining all of the vbv_delay values and making complicated computations."
370 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
372 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
373 examine the source code for one of the many open source projects that
374 already incorporate FFmpeg at (@url{projects.html}).
376 @section Can you support my C compiler XXX?
378 It depends. If your compiler is C99-compliant, then patches to support
379 it are likely to be welcome if they do not pollute the source code
380 with @code{#ifdef}s related to the compiler.
382 @section Is Microsoft Visual C++ supported?
384 No. Microsoft Visual C++ is not compliant to the C99 standard and does
385 not - among other things - support the inline assembly used in FFmpeg.
386 If you wish to use MSVC++ for your
387 project then you can link the MSVC++ code with libav* as long as
388 you compile the latter with a working C compiler. For more information, see
389 the @emph{Microsoft Visual C++ compatibility} section in the FFmpeg
392 There have been efforts to make FFmpeg compatible with MSVC++ in the
393 past. However, they have all been rejected as too intrusive, especially
394 since MinGW does the job adequately. None of the core developers
395 work with MSVC++ and thus this item is low priority. Should you find
396 the silver bullet that solves this problem, feel free to shoot it at us.
398 We strongly recommend you to move over from MSVC++ to MinGW tools.
400 @section Can I use FFmpeg or libavcodec under Windows?
402 Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg.
403 Read the @emph{Windows} section in the FFmpeg documentation to find more
406 To get help and instructions for building FFmpeg under Windows, check out
407 the FFmpeg Windows Help Forum at
408 @url{http://ffmpeg.arrozcru.org/}.
410 @section Can you add automake, libtool or autoconf support?
412 No. These tools are too bloated and they complicate the build.
414 @section Why not rewrite ffmpeg in object-oriented C++?
416 FFmpeg is already organized in a highly modular manner and does not need to
417 be rewritten in a formal object language. Further, many of the developers
418 favor straight C; it works for them. For more arguments on this matter,
419 read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
421 @section Why are the ffmpeg programs devoid of debugging symbols?
423 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
424 information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
425 you need the debug information, used the *_g versions.
427 @section I do not like the LGPL, can I contribute code under the GPL instead?
429 Yes, as long as the code is optional and can easily and cleanly be placed
430 under #if CONFIG_GPL without breaking anything. So for example a new codec
431 or filter would be OK under GPL while a bug fix to LGPL code would not.
433 @section I want to compile xyz.c alone but my compiler produced many errors.
435 Common code is in its own files in libav* and is used by the individual
436 codecs. They will not work without the common parts, you have to compile
437 the whole libav*. If you wish, disable some parts with configure switches.
438 You can also try to hack it and remove more, but if you had problems fixing
439 the compilation failure then you are probably not qualified for this.
441 @section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available.
443 FFmpeg is a pure C project, so to use the libraries within your C++ application
444 you need to explicitly state that you are using a C library. You can do this by
445 encompassing your FFmpeg includes using @code{extern "C"}.
447 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
449 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
451 You have to implement a URLProtocol, see @file{libavformat/file.c} in
452 FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer sources.
454 @section I get "No compatible shell script interpreter found." in MSys.
456 The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
458 @section I get "./configure: line <xxx>: pr: command not found" in MSys.
460 The standard MSys install doesn't come with pr. You need to get it from the coreutils package.
462 @section Where can I find libav* headers for Pascal/Delphi?
464 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
466 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
468 see @url{http://www.ffmpeg.org/~michael/}
470 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
472 Even if peculiar since it is network oriented, RTP is a container like any
473 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
474 In this specific case please look at RFC 4629 to see how it should be done.
476 @section AVStream.r_frame_rate is wrong, it is much larger than the framerate.
478 r_frame_rate is NOT the average framerate, it is the smallest framerate
479 that can accurately represent all timestamps. So no, it is not
480 wrong if it is larger than the average!
481 For example, if you have mixed 25 and 30 fps content, then r_frame_rate