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 Use the @option{-start_number} option to declare a starting number for
116 the sequence. This is useful if your sequence does not start with
117 @file{img001.jpg} but is still in a numerical order. The following
118 example will start with @file{img100.jpg}:
121 ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg
124 If you have large number of pictures to rename, you can use the
125 following command to ease the burden. The command, using the bourne
126 shell syntax, symbolically links all files in the current directory
127 that match @code{*jpg} to the @file{/tmp} directory in the sequence of
128 @file{img001.jpg}, @file{img002.jpg} and so on.
131 x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
134 If you want to sequence them by oldest modified first, substitute
135 @code{$(ls -r -t *jpg)} in place of @code{*jpg}.
140 ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
143 The same logic is used for any image format that ffmpeg reads.
145 You can also use @command{cat} to pipe images to ffmpeg:
148 cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg
151 @section How do I encode movie to single pictures?
156 ffmpeg -i movie.mpg movie%d.jpg
159 The @file{movie.mpg} used as input will be converted to
160 @file{movie1.jpg}, @file{movie2.jpg}, etc...
162 Instead of relying on file format self-recognition, you may also use
168 to force the encoding.
170 Applying that to the previous example:
172 ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg
175 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
177 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
179 For multithreaded MPEG* encoding, the encoded slices must be independent,
180 otherwise thread n would practically have to wait for n-1 to finish, so it's
181 quite logical that there is a small reduction of quality. This is not a bug.
183 @section How can I read from the standard input or write to the standard output?
185 Use @file{-} as file name.
187 @section -f jpeg doesn't work.
189 Try '-f image2 test%d.jpg'.
191 @section Why can I not change the frame rate?
193 Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates.
194 Choose a different codec with the -c:v command line option.
196 @section How do I encode Xvid or DivX video with ffmpeg?
198 Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
199 standard (note that there are many other coding formats that use this
200 same standard). Thus, use '-c:v mpeg4' to encode in these formats. The
201 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
202 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
203 force the fourcc 'xvid' to be stored as the video fourcc rather than the
206 @section Which are good parameters for encoding high quality MPEG-4?
208 '-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2',
209 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
211 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
213 '-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2'
214 but beware the '-g 100' might cause problems with some decoders.
215 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
217 @section Interlaced video looks very bad when encoded with ffmpeg, what is wrong?
219 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
220 material, and try '-top 0/1' if the result looks really messed-up.
222 @section How can I read DirectShow files?
224 If you have built FFmpeg with @code{./configure --enable-avisynth}
225 (only possible on MinGW/Cygwin platforms),
226 then you may use any file that DirectShow can read as input.
228 Just create an "input.avs" text file with this single line ...
230 DirectShowSource("C:\path to your file\yourfile.asf")
232 ... and then feed that text file to ffmpeg:
237 For ANY other help on AviSynth, please visit the
238 @uref{http://www.avisynth.org/, AviSynth homepage}.
240 @section How can I join video files?
242 To "join" video files is quite ambiguous. The following list explains the
243 different kinds of "joining" and points out how those are addressed in
244 FFmpeg. To join video files may mean:
249 To put them one after the other: this is called to @emph{concatenate} them
250 (in short: concat) and is addressed
251 @ref{How can I concatenate video files, in this very faq}.
254 To put them together in the same file, to let the user choose between the
255 different versions (example: different audio languages): this is called to
256 @emph{multiplex} them together (in short: mux), and is done by simply
257 invoking ffmpeg with several @option{-i} options.
260 For audio, to put all channels together in a single stream (example: two
261 mono streams into one stereo stream): this is sometimes called to
262 @emph{merge} them, and can be done using the
263 @url{http://ffmpeg.org/ffmpeg-filters.html#amerge, @code{amerge}} filter.
266 For audio, to play one on top of the other: this is called to @emph{mix}
267 them, and can be done by first merging them into a single stream and then
268 using the @url{http://ffmpeg.org/ffmpeg-filters.html#pan, @code{pan}} filter to mix
269 the channels at will.
272 For video, to display both together, side by side or one on top of a part of
273 the other; it can be done using the
274 @url{http://ffmpeg.org/ffmpeg-filters.html#overlay, @code{overlay}} video filter.
278 @anchor{How can I concatenate video files}
279 @section How can I concatenate video files?
281 There are several solutions, depending on the exact circumstances.
283 @subsection Concatenating using the concat @emph{filter}
285 FFmpeg has a @url{http://ffmpeg.org/ffmpeg-filters.html#concat,
286 @code{concat}} filter designed specifically for that, with examples in the
287 documentation. This operation is recommended if you need to re-encode.
289 @subsection Concatenating using the concat @emph{demuxer}
291 FFmpeg has a @url{http://www.ffmpeg.org/ffmpeg-formats.html#concat,
292 @code{concat}} demuxer which you can use when you want to avoid a re-encode and
293 your format doesn't support file level concatenation.
295 @subsection Concatenating using the concat @emph{protocol} (file level)
297 FFmpeg has a @url{http://ffmpeg.org/ffmpeg-protocols.html#concat,
298 @code{concat}} protocol designed specifically for that, with examples in the
301 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenate
302 video by merely concatenating the files containing them.
304 Hence you may concatenate your multimedia files by first transcoding them to
305 these privileged formats, then using the humble @code{cat} command (or the
306 equally humble @code{copy} under Windows), and finally transcoding back to your
310 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
311 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
312 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
313 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
316 Additionally, you can use the @code{concat} protocol instead of @code{cat} or
317 @code{copy} which will avoid creation of a potentially huge intermediate file.
320 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
321 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
322 ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg
323 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
326 Note that you may need to escape the character "|" which is special for many
329 Another option is usage of named pipes, should your platform support it:
332 mkfifo intermediate1.mpg
333 mkfifo intermediate2.mpg
334 ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null &
335 ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null &
336 cat intermediate1.mpg intermediate2.mpg |\
337 ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi
340 @subsection Concatenating using raw audio and video
342 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
343 allow concatenation, and the transcoding step is almost lossless.
344 When using multiple yuv4mpegpipe(s), the first line needs to be discarded
345 from all but the first stream. This can be accomplished by piping through
346 @code{tail} as seen below. Note that when piping through @code{tail} you
347 must use command grouping, @code{@{ ;@}}, to background properly.
349 For example, let's say we want to concatenate two FLV files into an
359 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
360 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
361 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
362 @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
363 cat temp1.a temp2.a > all.a &
364 cat temp1.v temp2.v > all.v &
365 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
366 -f yuv4mpegpipe -i all.v \
368 rm temp[12].[av] all.[av]
371 @section Using @option{-f lavfi}, audio becomes mono for no apparent reason.
373 Use @option{-dumpgraph -} to find out exactly where the channel layout is
376 Most likely, it is through @code{auto-inserted aresample}. Try to understand
377 why the converting filter was needed at that place.
379 Just before the output is a likely place, as @option{-f lavfi} currently
380 only support packed S16.
382 Then insert the correct @code{aformat} explicitly in the filtergraph,
383 specifying the exact format.
386 aformat=sample_fmts=s16:channel_layouts=stereo
389 @section Why does FFmpeg not see the subtitles in my VOB file?
391 VOB and a few other formats do not have a global header that describes
392 everything present in the file. Instead, applications are supposed to scan
393 the file to see what it contains. Since VOB files are frequently large, only
394 the beginning is scanned. If the subtitles happen only later in the file,
395 they will not be initally detected.
397 Some applications, including the @code{ffmpeg} command-line tool, can only
398 work with streams that were detected during the initial scan; streams that
399 are detected later are ignored.
401 The size of the initial scan is controlled by two options: @code{probesize}
402 (default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For
403 the subtitle stream to be detected, both values must be large enough.
405 @section Why was the @command{ffmpeg} @option{-sameq} option removed? What to use instead?
407 The @option{-sameq} option meant "same quantizer", and made sense only in a
408 very limited set of cases. Unfortunately, a lot of people mistook it for
409 "same quality" and used it in places where it did not make sense: it had
410 roughly the expected visible effect, but achieved it in a very inefficient
413 Each encoder has its own set of options to set the quality-vs-size balance,
414 use the options for the encoder you are using to set the quality level to a
415 point acceptable for your tastes. The most common options to do that are
416 @option{-qscale} and @option{-qmax}, but you should peruse the documentation
417 of the encoder you chose.
421 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
423 Yes. Check the @file{doc/examples} directory in the source
424 repository, also available online at:
425 @url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}.
427 Examples are also installed by default, usually in
428 @code{$PREFIX/share/ffmpeg/examples}.
430 Also you may read the Developers Guide of the FFmpeg documentation. Alternatively,
431 examine the source code for one of the many open source projects that
432 already incorporate FFmpeg at (@url{projects.html}).
434 @section Can you support my C compiler XXX?
436 It depends. If your compiler is C99-compliant, then patches to support
437 it are likely to be welcome if they do not pollute the source code
438 with @code{#ifdef}s related to the compiler.
440 @section Is Microsoft Visual C++ supported?
442 Yes. Please see the @uref{platform.html, Microsoft Visual C++}
443 section in the FFmpeg documentation.
445 @section Can you add automake, libtool or autoconf support?
447 No. These tools are too bloated and they complicate the build.
449 @section Why not rewrite FFmpeg in object-oriented C++?
451 FFmpeg is already organized in a highly modular manner and does not need to
452 be rewritten in a formal object language. Further, many of the developers
453 favor straight C; it works for them. For more arguments on this matter,
454 read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
456 @section Why are the ffmpeg programs devoid of debugging symbols?
458 The build process creates @command{ffmpeg_g}, @command{ffplay_g}, etc. which
459 contain full debug information. Those binaries are stripped to create
460 @command{ffmpeg}, @command{ffplay}, etc. If you need the debug information, use
463 @section I do not like the LGPL, can I contribute code under the GPL instead?
465 Yes, as long as the code is optional and can easily and cleanly be placed
466 under #if CONFIG_GPL without breaking anything. So, for example, a new codec
467 or filter would be OK under GPL while a bug fix to LGPL code would not.
469 @section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves.
471 FFmpeg builds static libraries by default. In static libraries, dependencies
472 are not handled. That has two consequences. First, you must specify the
473 libraries in dependency order: @code{-lavdevice} must come before
474 @code{-lavformat}, @code{-lavutil} must come after everything else, etc.
475 Second, external libraries that are used in FFmpeg have to be specified too.
477 An easy way to get the full list of required libraries in dependency order
478 is to use @code{pkg-config}.
481 c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec)
484 See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for
487 @section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.
489 FFmpeg is a pure C project, so to use the libraries within your C++ application
490 you need to explicitly state that you are using a C library. You can do this by
491 encompassing your FFmpeg includes using @code{extern "C"}.
493 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
495 @section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope
497 FFmpeg is a pure C project using C99 math features, in order to enable C++
498 to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS
500 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
502 You have to create a custom AVIOContext using @code{avio_alloc_context},
503 see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources.
505 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
507 see @url{http://www.ffmpeg.org/~michael/}
509 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
511 Even if peculiar since it is network oriented, RTP is a container like any
512 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
513 In this specific case please look at RFC 4629 to see how it should be done.
515 @section AVStream.r_frame_rate is wrong, it is much larger than the frame rate.
517 @code{r_frame_rate} is NOT the average frame rate, it is the smallest frame rate
518 that can accurately represent all timestamps. So no, it is not
519 wrong if it is larger than the average!
520 For example, if you have mixed 25 and 30 fps content, then @code{r_frame_rate}
521 will be 150 (it is the least common multiple).
522 If you are looking for the average frame rate, see @code{AVStream.avg_frame_rate}.
524 @section Why is @code{make fate} not running all tests?
526 Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable
527 or @code{FATE_SAMPLES} environment variable or the @code{--samples}
528 @command{configure} option is set to the right path.
530 @section Why is @code{make fate} not finding the samples?
532 Do you happen to have a @code{~} character in the samples path to indicate a
533 home directory? The value is used in ways where the shell cannot expand it,
534 causing FATE to not find files. Just replace @code{~} by the full path.