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 bug report/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 You may view our mailing lists with a more forum-alike look here:
62 @url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user},
63 but, if you post, please remember that our mailing list rules still apply there.
65 @section I cannot read this file although this format seems to be supported by ffmpeg.
67 Even if ffmpeg can read the container format, it may not support all its
68 codecs. Please consult the supported codec list in the ffmpeg
71 @section Which codecs are supported by Windows?
73 Windows does not support standard formats like MPEG very well, unless you
74 install some additional codecs.
76 The following list of video codecs should work on most Windows systems:
87 Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
91 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
92 be mentioned that Microsoft claims a patent on the ASF format, and may sue
93 or threaten users who create ASF files with non-Microsoft software. It is
94 strongly advised to avoid ASF where possible.
96 The following list of audio codecs should work on most Windows systems:
103 If some MP3 codec like LAME is installed.
109 @section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}
111 This is a bug in gcc. Do not report it to us. Instead, please report it to
112 the gcc developers. Note that we will not add workarounds for gcc bugs.
114 Also note that (some of) the gcc developers believe this is not a bug or
115 not a bug they should fix:
116 @url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}.
117 Then again, some of them do not know the difference between an undecidable
118 problem and an NP-hard problem...
122 @section ffmpeg does not work; what is wrong?
124 Try a @code{make distclean} in the ffmpeg source directory before the build. If this does not help see
125 (@url{http://ffmpeg.org/bugreports.html}).
127 @section How do I encode single pictures into movies?
129 First, rename your pictures to follow a numerical sequence.
130 For example, img1.jpg, img2.jpg, img3.jpg,...
134 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
137 Notice that @samp{%d} is replaced by the image number.
139 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
141 The same logic is used for any image format that ffmpeg reads.
143 @section How do I encode movie to single pictures?
148 ffmpeg -i movie.mpg movie%d.jpg
151 The @file{movie.mpg} used as input will be converted to
152 @file{movie1.jpg}, @file{movie2.jpg}, etc...
154 Instead of relying on file format self-recognition, you may also use
160 to force the encoding.
162 Applying that to the previous example:
164 ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
167 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
169 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
171 For multithreaded MPEG* encoding, the encoded slices must be independent,
172 otherwise thread n would practically have to wait for n-1 to finish, so it's
173 quite logical that there is a small reduction of quality. This is not a bug.
175 @section How can I read from the standard input or write to the standard output?
177 Use @file{-} as file name.
179 @section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
181 This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
182 (@url{http://svn.ffmpeg.org/michael/trunk/patches/bttv-420-2.4.26.patch?view=co}). This may also
183 apply cleanly to other 2.4-series kernels.
185 @section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
187 Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
188 will cause somewhat too strong filtering. A fix is to apply (@url{http://svn.ffmpeg.org/michael/trunk/patches/bttv-comb-2.4.26.patch?view=co})
189 or (@url{http://svn.ffmpeg.org/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co})
190 and pass 'combfilter=2'.
192 @section -f jpeg doesn't work.
194 Try '-f image2 test%d.jpg'.
196 @section Why can I not change the framerate?
198 Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
199 Choose a different codec with the -vcodec command line option.
201 @section How do I encode Xvid or DivX video with ffmpeg?
203 Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
204 standard (note that there are many other coding formats that use this
205 same standard). Thus, use '-vcodec mpeg4' to encode in these formats. The
206 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
207 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
208 force the fourcc 'xvid' to be stored as the video fourcc rather than the
211 @section How do I encode videos which play on the iPod?
215 -acodec libfaac -vcodec mpeg4 width<=320 height<=240
218 @item non-working stuff
220 @item example command line
221 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 -title X output.mp4
224 @section How do I encode videos which play on the PSP?
228 -acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
231 @item non-working stuff
233 @item example command line
234 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 -title X -f psp output.mp4
235 @item needed stuff for H.264
236 -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
237 @item working stuff for H.264
239 @item non-working stuff for H.264
241 @item example command line
242 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 -title X -f psp -flags loop -trellis 2 -partitions parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 output.mp4
243 @item higher resolution for newer PSP firmwares, width<=480, height<=272
244 -vcodec libx264 -level 21 -coder 1 -f psp
245 @item example command line
246 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
249 @section Which are good parameters for encoding high quality MPEG-4?
251 '-mbd rd -flags +4mv+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2',
252 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
254 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
256 '-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2'
257 but beware the '-g 100' might cause problems with some decoders.
258 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
260 @section Interlaced video looks very bad when encoded with ffmpeg, what is wrong?
262 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
263 material, and try '-top 0/1' if the result looks really messed-up.
265 @section How can I read DirectShow files?
267 If you have built FFmpeg with @code{./configure --enable-avisynth}
268 (only possible on MinGW/Cygwin platforms),
269 then you may use any file that DirectShow can read as input.
270 (Be aware that this feature has been recently added,
271 so you will need to help yourself in case of problems.)
273 Just create an "input.avs" text file with this single line ...
275 DirectShowSource("C:\path to your file\yourfile.asf")
277 ... and then feed that text file to FFmpeg:
282 For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
284 @section How can I join video files?
286 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
287 merely concatenating them.
289 Hence you may concatenate your multimedia files by first transcoding them to
290 these privileged formats, then using the humble @code{cat} command (or the
291 equally humble @code{copy} under Windows), and finally transcoding back to your
295 ffmpeg -i input1.avi -sameq intermediate1.mpg
296 ffmpeg -i input2.avi -sameq intermediate2.mpg
297 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
298 ffmpeg -i intermediate_all.mpg -sameq output.avi
301 Notice that you should either use @code{-sameq} or set a reasonably high
302 bitrate for your intermediate and output files, if you want to preserve
305 Also notice that you may avoid the huge intermediate files by taking advantage
306 of named pipes, should your platform support it:
309 mkfifo intermediate1.mpg
310 mkfifo intermediate2.mpg
311 ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null &
312 ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null &
313 cat intermediate1.mpg intermediate2.mpg |\
314 ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi
317 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
318 allow concatenation, and the transcoding step is almost lossless.
320 For example, let's say we want to join two FLV files into an output.flv file:
329 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
330 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
331 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
332 ffmpeg -i input2.flv -an -f yuv4mpegpipe - > temp2.v < /dev/null &
333 cat temp1.a temp2.a > all.a &
334 cat temp1.v temp2.v > all.v &
335 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
336 -f yuv4mpegpipe -i all.v \
338 rm temp[12].[av] all.[av]
341 @section FFmpeg does not adhere to the -maxrate setting, some frames are bigger than maxrate/fps.
343 Read the MPEG spec about video buffer verifier.
345 @section I want CBR, but no matter what I do frame sizes differ.
347 You do not understand what CBR is, please read the MPEG spec.
348 Read about video buffer verifier and constant bitrate.
349 The one sentence summary is that there is a buffer and the input rate is
350 constant, the output can vary as needed.
352 @section How do I check if a stream is CBR?
354 To quote the MPEG-2 spec:
355 "There is no way to tell that a bitstream is constant bitrate without
356 examining all of the vbv_delay values and making complicated computations."
361 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
363 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
364 examine the source code for one of the many open source projects that
365 already incorporate FFmpeg at (@url{projects.html}).
367 @section Can you support my C compiler XXX?
369 It depends. If your compiler is C99-compliant, then patches to support
370 it are likely to be welcome if they do not pollute the source code
371 with @code{#ifdef}s related to the compiler.
373 @section Is Microsoft Visual C++ supported?
375 No. Microsoft Visual C++ is not compliant to the C99 standard and does
376 not - among other things - support the inline assembly used in FFmpeg.
377 If you wish to use MSVC++ for your
378 project then you can link the MSVC++ code with libav* as long as
379 you compile the latter with a working C compiler. For more information, see
380 the @emph{Microsoft Visual C++ compatibility} section in the FFmpeg
383 There have been efforts to make FFmpeg compatible with MSVC++ in the
384 past. However, they have all been rejected as too intrusive, especially
385 since MinGW does the job adequately. None of the core developers
386 work with MSVC++ and thus this item is low priority. Should you find
387 the silver bullet that solves this problem, feel free to shoot it at us.
389 We strongly recommend you to move over from MSVC++ to MinGW tools.
391 @section Can I use FFmpeg or libavcodec under Windows?
393 Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg.
394 Read the @emph{Windows} section in the FFmpeg documentation to find more
397 To get help and instructions for building FFmpeg under Windows, check out
398 the FFmpeg Windows Help Forum at
399 @url{http://ffmpeg.arrozcru.org/}.
401 @section Can you add automake, libtool or autoconf support?
403 No. These tools are too bloated and they complicate the build.
405 @section Why not rewrite ffmpeg in object-oriented C++?
407 FFmpeg is already organized in a highly modular manner and does not need to
408 be rewritten in a formal object language. Further, many of the developers
409 favor straight C; it works for them. For more arguments on this matter,
410 read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
412 @section Why are the ffmpeg programs devoid of debugging symbols?
414 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
415 information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
416 you need the debug information, used the *_g versions.
418 @section I do not like the LGPL, can I contribute code under the GPL instead?
420 Yes, as long as the code is optional and can easily and cleanly be placed
421 under #if CONFIG_GPL without breaking anything. So for example a new codec
422 or filter would be OK under GPL while a bug fix to LGPL code would not.
424 @section I want to compile xyz.c alone but my compiler produced many errors.
426 Common code is in its own files in libav* and is used by the individual
427 codecs. They will not work without the common parts, you have to compile
428 the whole libav*. If you wish, disable some parts with configure switches.
429 You can also try to hack it and remove more, but if you had problems fixing
430 the compilation failure then you are probably not qualified for this.
432 @section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available.
434 FFmpeg is a pure C project, so to use the libraries within your C++ application
435 you need to explicitly state that you are using a C library. You can do this by
436 encompassing your FFmpeg includes using @code{extern "C"}.
438 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
440 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
442 You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
443 and libmpdemux/demux_lavf.c in MPlayer sources.
445 @section I get "No compatible shell script interpreter found." in MSys.
447 The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
449 @section I get "./configure: line <xxx>: pr: command not found" in MSys.
451 The standard MSys install doesn't come with pr. You need to get it from the coreutils package.
453 @section I tried to pass RTP packets into a decoder, but it doesn't work.
455 RTP is a container format like any other, you must first depacketize the
456 codec frames/samples stored in RTP and then feed to the decoder.
458 @section Where can I find libav* headers for Pascal/Delphi?
460 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
462 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
464 see @url{http://svn.ffmpeg.org/michael/trunk/docs/}
466 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
468 Even if peculiar since it is network oriented, RTP is a container like any
469 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
470 In this specific case please look at RFC 4629 to see how it should be done.
472 @section AVStream.r_frame_rate is wrong, it is much larger than the framerate.
474 r_frame_rate is NOT the average framerate, it is the smallest framerate
475 that can accurately represent all timestamps. So no, it is not
476 wrong if it is larger than the average!
477 For example, if you have mixed 25 and 30 fps content, then r_frame_rate