1 \input texinfo @c -*- texinfo -*-
5 @center @titlefont{FFmpeg FAQ}
12 @chapter General Questions
14 @section Why doesn't FFmpeg support feature [xyz]?
16 Because no one has taken on that task yet. FFmpeg development is
17 driven by the tasks that are important to the individual developers.
18 If there is a feature that is important to you, the best way to get
19 it implemented is to undertake the task yourself or sponsor a developer.
21 @section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?
23 No. Windows DLLs are not portable, bloated and often slow.
24 Moreover FFmpeg strives to support all codecs natively.
25 A DLL loader is not conducive to that goal.
27 @section I cannot read this file although this format seems to be supported by ffmpeg.
29 Even if ffmpeg can read the container format, it may not support all its
30 codecs. Please consult the supported codec list in the ffmpeg
33 @section Which codecs are supported by Windows?
35 Windows does not support standard formats like MPEG very well, unless you
36 install some additional codecs.
38 The following list of video codecs should work on most Windows systems:
49 Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
53 Note, ASF files often have .wmv or .wma extensions in Windows. It should also
54 be mentioned that Microsoft claims a patent on the ASF format, and may sue
55 or threaten users who create ASF files with non-Microsoft software. It is
56 strongly advised to avoid ASF where possible.
58 The following list of audio codecs should work on most Windows systems:
65 If some MP3 codec like LAME is installed.
71 @section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}
73 This is a bug in gcc. Do not report it to us. Instead, please report it to
74 the gcc developers. Note that we will not add workarounds for gcc bugs.
76 Also note that (some of) the gcc developers believe this is not a bug or
77 not a bug they should fix:
78 @url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}.
79 Then again, some of them do not know the difference between an undecidable
80 problem and an NP-hard problem...
82 @section I have installed this library with my distro's package manager. Why does @command{configure} not see it?
84 Distributions usually split libraries in several packages. The main package
85 contains the files necessary to run programs using the library. The
86 development package contains the files necessary to build programs using the
87 library. Sometimes, docs and/or data are in a separate package too.
89 To build FFmpeg, you need to install the development package. It is usually
90 called @file{libfoo-dev} or @file{libfoo-devel}. You can remove it after the
91 build is finished, but be sure to keep the main package.
95 @section ffmpeg does not work; what is wrong?
97 Try a @code{make distclean} in the ffmpeg source directory before the build.
98 If this does not help see
99 (@url{http://ffmpeg.org/bugreports.html}).
101 @section How do I encode single pictures into movies?
103 First, rename your pictures to follow a numerical sequence.
104 For example, img1.jpg, img2.jpg, img3.jpg,...
108 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
111 Notice that @samp{%d} is replaced by the image number.
113 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
115 If you have large number of pictures to rename, you can use the
116 following command to ease the burden. The command, using the bourne
117 shell syntax, symbolically links all files in the current directory
118 that match @code{*jpg} to the @file{/tmp} directory in the sequence of
119 @file{img001.jpg}, @file{img002.jpg} and so on.
122 x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
125 If you want to sequence them by oldest modified first, substitute
126 @code{$(ls -r -t *jpg)} in place of @code{*jpg}.
131 ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
134 The same logic is used for any image format that ffmpeg reads.
136 @section How do I encode movie to single pictures?
141 ffmpeg -i movie.mpg movie%d.jpg
144 The @file{movie.mpg} used as input will be converted to
145 @file{movie1.jpg}, @file{movie2.jpg}, etc...
147 Instead of relying on file format self-recognition, you may also use
153 to force the encoding.
155 Applying that to the previous example:
157 ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg
160 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
162 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
164 For multithreaded MPEG* encoding, the encoded slices must be independent,
165 otherwise thread n would practically have to wait for n-1 to finish, so it's
166 quite logical that there is a small reduction of quality. This is not a bug.
168 @section How can I read from the standard input or write to the standard output?
170 Use @file{-} as file name.
172 @section -f jpeg doesn't work.
174 Try '-f image2 test%d.jpg'.
176 @section Why can I not change the frame rate?
178 Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates.
179 Choose a different codec with the -c:v command line option.
181 @section How do I encode Xvid or DivX video with ffmpeg?
183 Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
184 standard (note that there are many other coding formats that use this
185 same standard). Thus, use '-c:v mpeg4' to encode in these formats. The
186 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
187 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
188 force the fourcc 'xvid' to be stored as the video fourcc rather than the
191 @section Which are good parameters for encoding high quality MPEG-4?
193 '-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2',
194 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
196 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
198 '-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2'
199 but beware the '-g 100' might cause problems with some decoders.
200 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
202 @section Interlaced video looks very bad when encoded with ffmpeg, what is wrong?
204 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
205 material, and try '-top 0/1' if the result looks really messed-up.
207 @section How can I read DirectShow files?
209 If you have built FFmpeg with @code{./configure --enable-avisynth}
210 (only possible on MinGW/Cygwin platforms),
211 then you may use any file that DirectShow can read as input.
213 Just create an "input.avs" text file with this single line ...
215 DirectShowSource("C:\path to your file\yourfile.asf")
217 ... and then feed that text file to ffmpeg:
222 For ANY other help on Avisynth, please visit the
223 @uref{http://www.avisynth.org/, Avisynth homepage}.
225 @section How can I join video files?
227 To "join" video files is quite ambiguous. The following list explains the
228 different kinds of "joining" and points out how those are addressed in
229 FFmpeg. To join video files may mean:
234 To put them one after the other: this is called to @emph{concatenate} them
235 (in short: concat) and is addressed
236 @ref{How can I concatenate video files, in this very faq}.
239 To put them together in the same file, to let the user choose between the
240 different versions (example: different audio languages): this is called to
241 @emph{multiplex} them together (in short: mux), and is done by simply
242 invoking ffmpeg with several @option{-i} options.
245 For audio, to put all channels together in a single stream (example: two
246 mono streams into one stereo stream): this is sometimes called to
247 @emph{merge} them, and can be done using the
248 @url{http://ffmpeg.org/ffmpeg.html#amerge, @code{amerge}} filter.
251 For audio, to play one on top of the other: this is called to @emph{mix}
252 them, and can be done by first merging them into a single stream and then
253 using the @url{http://ffmpeg.org/ffmpeg.html#pan, @code{pan}} filter to mix
254 the channels at will.
257 For video, to display both together, side by side or one on top of a part of
258 the other; it can be done using the
259 @url{http://ffmpeg.org/ffmpeg.html#overlay, @code{overlay}} video filter.
263 @anchor{How can I concatenate video files}
264 @section How can I concatenate video files?
266 There are several solutions, depending on the exact circumstances.
268 @subsection Concatenating using filters
270 FFmpeg has a @url{http://ffmpeg.org/ffmpeg.html#concat-1, @code{concat}}
271 filter designed specifically for that, with examples in the documentation.
273 @subsection Concatenating at the file level
275 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenate
276 video by merely concatenating the files them.
278 Hence you may concatenate your multimedia files by first transcoding them to
279 these privileged formats, then using the humble @code{cat} command (or the
280 equally humble @code{copy} under Windows), and finally transcoding back to your
284 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
285 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
286 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
287 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
290 Additionally, you can use the @code{concat} protocol instead of @code{cat} or
291 @code{copy} which will avoid creation of a potentially huge intermediate file.
294 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
295 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
296 ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg
297 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
300 Note that you may need to escape the character "|" which is special for many
303 Another option is usage of named pipes, should your platform support it:
306 mkfifo intermediate1.mpg
307 mkfifo intermediate2.mpg
308 ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null &
309 ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null &
310 cat intermediate1.mpg intermediate2.mpg |\
311 ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi
314 @subsection Concatenating using raw audio and video
316 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
317 allow concatenation, and the transcoding step is almost lossless.
318 When using multiple yuv4mpegpipe(s), the first line needs to be discarded
319 from all but the first stream. This can be accomplished by piping through
320 @code{tail} as seen below. Note that when piping through @code{tail} you
321 must use command grouping, @code{@{ ;@}}, to background properly.
323 For example, let's say we want to concatenate two FLV files into an
333 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
334 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
335 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
336 @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
337 cat temp1.a temp2.a > all.a &
338 cat temp1.v temp2.v > all.v &
339 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
340 -f yuv4mpegpipe -i all.v \
342 rm temp[12].[av] all.[av]
345 @section -profile option fails when encoding H.264 video with AAC audio
347 @command{ffmpeg} prints an error like
350 Undefined constant or missing '(' in 'baseline'
351 Unable to parse option value "baseline"
352 Error setting option profile to value baseline.
355 Short answer: write @option{-profile:v} instead of @option{-profile}.
357 Long answer: this happens because the @option{-profile} option can apply to both
358 video and audio. Specifically the AAC encoder also defines some profiles, none
359 of which are named @var{baseline}.
361 The solution is to apply the @option{-profile} option to the video stream only
362 by using @url{http://ffmpeg.org/ffmpeg.html#Stream-specifiers-1, Stream specifiers}.
363 Appending @code{:v} to it will do exactly that.
365 @section Using @option{-f lavfi}, audio becomes mono for no apparent reason.
367 Use @option{-dumpgraph -} to find out exactly where the channel layout is
370 Most likely, it is through @code{auto-inserted aconvert}. Try to understand
371 why the converting filter was needed at that place.
373 Just before the output is a likely place, as @option{-f lavfi} currently
374 only support packed S16.
376 Then insert the correct @code{aconvert} explicitly in the filter graph,
377 specifying the exact format.
380 aconvert=s16:stereo:packed
383 @section Why does FFmpeg not see the subtitles in my VOB file?
385 VOB and a few other formats do not have a global header that describes
386 everything present in the file. Instead, applications are supposed to scan
387 the file to see what it contains. Since VOB files are frequently large, only
388 the beginning is scanned. If the subtitles happen only later in the file,
389 they will not be initally detected.
391 Some applications, including the @code{ffmpeg} command-line tool, can only
392 work with streams that were detected during the initial scan; streams that
393 are detected later are ignored.
395 The size of the initial scan is controlled by two options: @code{probesize}
396 (default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For
397 the subtitle stream to be detected, both values must be large enough.
399 @section Why was the @command{ffmpeg} @option{-sameq} option removed? What to use instead?
401 The @option{-sameq} option meant "same quantizer", and made sense only in a
402 very limited set of cases. Unfortunately, a lot of people mistook it for
403 "same quality" and used it in places where it did not make sense: it had
404 roughly the expected visible effect, but achieved it in a very inefficient
407 Each encoder has its own set of options to set the quality-vs-size balance,
408 use the options for the encoder you are using to set the quality level to a
409 point acceptable for your tastes. The most common options to do that are
410 @option{-qscale} and @option{-qmax}, but you should peruse the documentation
411 of the encoder you chose.
415 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
417 Yes. Check the @file{doc/examples} directory in the source
418 repository, also available online at:
419 @url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}.
421 Examples are also installed by default, usually in
422 @code{$PREFIX/share/ffmpeg/examples}.
424 Also you may read the Developers Guide of the FFmpeg documentation. Alternatively,
425 examine the source code for one of the many open source projects that
426 already incorporate FFmpeg at (@url{projects.html}).
428 @section Can you support my C compiler XXX?
430 It depends. If your compiler is C99-compliant, then patches to support
431 it are likely to be welcome if they do not pollute the source code
432 with @code{#ifdef}s related to the compiler.
434 @section Is Microsoft Visual C++ supported?
436 Yes. Please see the @uref{platform.html, Microsoft Visual C++}
437 section in the FFmpeg documentation.
439 @section Can you add automake, libtool or autoconf support?
441 No. These tools are too bloated and they complicate the build.
443 @section Why not rewrite FFmpeg in object-oriented C++?
445 FFmpeg is already organized in a highly modular manner and does not need to
446 be rewritten in a formal object language. Further, many of the developers
447 favor straight C; it works for them. For more arguments on this matter,
448 read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
450 @section Why are the ffmpeg programs devoid of debugging symbols?
452 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
453 information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
454 you need the debug information, use the *_g versions.
456 @section I do not like the LGPL, can I contribute code under the GPL instead?
458 Yes, as long as the code is optional and can easily and cleanly be placed
459 under #if CONFIG_GPL without breaking anything. So, for example, a new codec
460 or filter would be OK under GPL while a bug fix to LGPL code would not.
462 @section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves.
464 FFmpeg builds static libraries by default. In static libraries, dependencies
465 are not handled. That has two consequences. First, you must specify the
466 libraries in dependency order: @code{-lavdevice} must come before
467 @code{-lavformat}, @code{-lavutil} must come after everything else, etc.
468 Second, external libraries that are used in FFmpeg have to be specified too.
470 An easy way to get the full list of required libraries in dependency order
471 is to use @code{pkg-config}.
474 c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec)
477 See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for
480 @section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.
482 FFmpeg is a pure C project, so to use the libraries within your C++ application
483 you need to explicitly state that you are using a C library. You can do this by
484 encompassing your FFmpeg includes using @code{extern "C"}.
486 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
488 @section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope
490 FFmpeg is a pure C project using C99 math features, in order to enable C++
491 to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS
493 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
495 You have to create a custom AVIOContext using @code{avio_alloc_context},
496 see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources.
498 @section Where can I find libav* headers for Pascal/Delphi?
500 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
502 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
504 see @url{http://www.ffmpeg.org/~michael/}
506 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
508 Even if peculiar since it is network oriented, RTP is a container like any
509 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
510 In this specific case please look at RFC 4629 to see how it should be done.
512 @section AVStream.r_frame_rate is wrong, it is much larger than the frame rate.
514 r_frame_rate is NOT the average frame rate, it is the smallest frame rate
515 that can accurately represent all timestamps. So no, it is not
516 wrong if it is larger than the average!
517 For example, if you have mixed 25 and 30 fps content, then r_frame_rate
520 @section Why is @code{make fate} not running all tests?
522 Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable
523 or @code{FATE_SAMPLES} environment variable or the @code{--samples}
524 @command{configure} option is set to the right path.
526 @section Why is @code{make fate} not finding the samples?
528 Do you happen to have a @code{~} character in the samples path to indicate a
529 home directory? The value is used in ways where the shell cannot expand it,
530 causing FATE to not find files. Just replace @code{~} by the full path.