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.
93 @section How do I make @command{pkg-config} find my libraries?
95 Somewhere along with your libraries, there is a @file{.pc} file (or several)
96 in a @file{pkgconfig} directory. You need to set environment variables to
97 point @command{pkg-config} to these files.
99 If you need to @emph{add} directories to @command{pkg-config}'s search list
100 (typical use case: library installed separately), add it to
101 @code{$PKG_CONFIG_PATH}:
104 export PKG_CONFIG_PATH=/opt/x264/lib/pkgconfig:/opt/opus/lib/pkgconfig
107 If you need to @emph{replace} @command{pkg-config}'s search list
108 (typical use case: cross-compiling), set it in
109 @code{$PKG_CONFIG_LIBDIR}:
112 export PKG_CONFIG_LIBDIR=/home/me/cross/usr/lib/pkgconfig:/home/me/cross/usr/local/lib/pkgconfig
115 If you need to know the library's internal dependencies (typical use: static
116 linking), add the @code{--static} option to @command{pkg-config}:
119 ./configure --pkg-config-flags=--static
122 @section How do I use @command{pkg-config} when cross-compiling?
124 The best way is to install @command{pkg-config} in your cross-compilation
125 environment. It will automatically use the cross-compilation libraries.
127 You can also use @command{pkg-config} from the host environment by
128 specifying explicitly @code{--pkg-config=pkg-config} to @command{configure}.
129 In that case, you must point @command{pkg-config} to the correct directories
130 using the @code{PKG_CONFIG_LIBDIR}, as explained in the previous entry.
132 As an intermediate solution, you can place in your cross-compilation
133 environment a script that calls the host @command{pkg-config} with
134 @code{PKG_CONFIG_LIBDIR} set. That script can look like that:
138 PKG_CONFIG_LIBDIR=/path/to/cross/lib/pkgconfig
139 export PKG_CONFIG_LIBDIR
140 exec /usr/bin/pkg-config "$@@"
145 @section ffmpeg does not work; what is wrong?
147 Try a @code{make distclean} in the ffmpeg source directory before the build.
148 If this does not help see
149 (@url{http://ffmpeg.org/bugreports.html}).
151 @section How do I encode single pictures into movies?
153 First, rename your pictures to follow a numerical sequence.
154 For example, img1.jpg, img2.jpg, img3.jpg,...
158 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
161 Notice that @samp{%d} is replaced by the image number.
163 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc.
165 Use the @option{-start_number} option to declare a starting number for
166 the sequence. This is useful if your sequence does not start with
167 @file{img001.jpg} but is still in a numerical order. The following
168 example will start with @file{img100.jpg}:
171 ffmpeg -f image2 -start_number 100 -i img%d.jpg /tmp/a.mpg
174 If you have large number of pictures to rename, you can use the
175 following command to ease the burden. The command, using the bourne
176 shell syntax, symbolically links all files in the current directory
177 that match @code{*jpg} to the @file{/tmp} directory in the sequence of
178 @file{img001.jpg}, @file{img002.jpg} and so on.
181 x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
184 If you want to sequence them by oldest modified first, substitute
185 @code{$(ls -r -t *jpg)} in place of @code{*jpg}.
190 ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
193 The same logic is used for any image format that ffmpeg reads.
195 You can also use @command{cat} to pipe images to ffmpeg:
198 cat *.jpg | ffmpeg -f image2pipe -c:v mjpeg -i - output.mpg
201 @section How do I encode movie to single pictures?
206 ffmpeg -i movie.mpg movie%d.jpg
209 The @file{movie.mpg} used as input will be converted to
210 @file{movie1.jpg}, @file{movie2.jpg}, etc...
212 Instead of relying on file format self-recognition, you may also use
218 to force the encoding.
220 Applying that to the previous example:
222 ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg
225 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
227 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
229 For multithreaded MPEG* encoding, the encoded slices must be independent,
230 otherwise thread n would practically have to wait for n-1 to finish, so it's
231 quite logical that there is a small reduction of quality. This is not a bug.
233 @section How can I read from the standard input or write to the standard output?
235 Use @file{-} as file name.
237 @section -f jpeg doesn't work.
239 Try '-f image2 test%d.jpg'.
241 @section Why can I not change the frame rate?
243 Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates.
244 Choose a different codec with the -c:v command line option.
246 @section How do I encode Xvid or DivX video with ffmpeg?
248 Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
249 standard (note that there are many other coding formats that use this
250 same standard). Thus, use '-c:v mpeg4' to encode in these formats. The
251 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
252 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
253 force the fourcc 'xvid' to be stored as the video fourcc rather than the
256 @section Which are good parameters for encoding high quality MPEG-4?
258 '-mbd rd -flags +mv4+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 the
288 @uref{http://www.avisynth.org/, AviSynth homepage}.
290 @section How can I join video files?
292 To "join" video files is quite ambiguous. The following list explains the
293 different kinds of "joining" and points out how those are addressed in
294 FFmpeg. To join video files may mean:
299 To put them one after the other: this is called to @emph{concatenate} them
300 (in short: concat) and is addressed
301 @ref{How can I concatenate video files, in this very faq}.
304 To put them together in the same file, to let the user choose between the
305 different versions (example: different audio languages): this is called to
306 @emph{multiplex} them together (in short: mux), and is done by simply
307 invoking ffmpeg with several @option{-i} options.
310 For audio, to put all channels together in a single stream (example: two
311 mono streams into one stereo stream): this is sometimes called to
312 @emph{merge} them, and can be done using the
313 @url{http://ffmpeg.org/ffmpeg-filters.html#amerge, @code{amerge}} filter.
316 For audio, to play one on top of the other: this is called to @emph{mix}
317 them, and can be done by first merging them into a single stream and then
318 using the @url{http://ffmpeg.org/ffmpeg-filters.html#pan, @code{pan}} filter to mix
319 the channels at will.
322 For video, to display both together, side by side or one on top of a part of
323 the other; it can be done using the
324 @url{http://ffmpeg.org/ffmpeg-filters.html#overlay, @code{overlay}} video filter.
328 @anchor{How can I concatenate video files}
329 @section How can I concatenate video files?
331 There are several solutions, depending on the exact circumstances.
333 @subsection Concatenating using the concat @emph{filter}
335 FFmpeg has a @url{http://ffmpeg.org/ffmpeg-filters.html#concat,
336 @code{concat}} filter designed specifically for that, with examples in the
337 documentation. This operation is recommended if you need to re-encode.
339 @subsection Concatenating using the concat @emph{demuxer}
341 FFmpeg has a @url{http://www.ffmpeg.org/ffmpeg-formats.html#concat,
342 @code{concat}} demuxer which you can use when you want to avoid a re-encode and
343 your format doesn't support file level concatenation.
345 @subsection Concatenating using the concat @emph{protocol} (file level)
347 FFmpeg has a @url{http://ffmpeg.org/ffmpeg-protocols.html#concat,
348 @code{concat}} protocol designed specifically for that, with examples in the
351 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenate
352 video by merely concatenating the files containing them.
354 Hence you may concatenate your multimedia files by first transcoding them to
355 these privileged formats, then using the humble @code{cat} command (or the
356 equally humble @code{copy} under Windows), and finally transcoding back to your
360 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
361 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
362 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
363 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
366 Additionally, you can use the @code{concat} protocol instead of @code{cat} or
367 @code{copy} which will avoid creation of a potentially huge intermediate file.
370 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
371 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
372 ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg
373 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
376 Note that you may need to escape the character "|" which is special for many
379 Another option is usage of named pipes, should your platform support it:
382 mkfifo intermediate1.mpg
383 mkfifo intermediate2.mpg
384 ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null &
385 ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null &
386 cat intermediate1.mpg intermediate2.mpg |\
387 ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi
390 @subsection Concatenating using raw audio and video
392 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
393 allow concatenation, and the transcoding step is almost lossless.
394 When using multiple yuv4mpegpipe(s), the first line needs to be discarded
395 from all but the first stream. This can be accomplished by piping through
396 @code{tail} as seen below. Note that when piping through @code{tail} you
397 must use command grouping, @code{@{ ;@}}, to background properly.
399 For example, let's say we want to concatenate two FLV files into an
409 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
410 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
411 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
412 @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
413 cat temp1.a temp2.a > all.a &
414 cat temp1.v temp2.v > all.v &
415 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
416 -f yuv4mpegpipe -i all.v \
418 rm temp[12].[av] all.[av]
421 @section Using @option{-f lavfi}, audio becomes mono for no apparent reason.
423 Use @option{-dumpgraph -} to find out exactly where the channel layout is
426 Most likely, it is through @code{auto-inserted aresample}. Try to understand
427 why the converting filter was needed at that place.
429 Just before the output is a likely place, as @option{-f lavfi} currently
430 only support packed S16.
432 Then insert the correct @code{aformat} explicitly in the filtergraph,
433 specifying the exact format.
436 aformat=sample_fmts=s16:channel_layouts=stereo
439 @section Why does FFmpeg not see the subtitles in my VOB file?
441 VOB and a few other formats do not have a global header that describes
442 everything present in the file. Instead, applications are supposed to scan
443 the file to see what it contains. Since VOB files are frequently large, only
444 the beginning is scanned. If the subtitles happen only later in the file,
445 they will not be initially detected.
447 Some applications, including the @code{ffmpeg} command-line tool, can only
448 work with streams that were detected during the initial scan; streams that
449 are detected later are ignored.
451 The size of the initial scan is controlled by two options: @code{probesize}
452 (default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For
453 the subtitle stream to be detected, both values must be large enough.
455 @section Why was the @command{ffmpeg} @option{-sameq} option removed? What to use instead?
457 The @option{-sameq} option meant "same quantizer", and made sense only in a
458 very limited set of cases. Unfortunately, a lot of people mistook it for
459 "same quality" and used it in places where it did not make sense: it had
460 roughly the expected visible effect, but achieved it in a very inefficient
463 Each encoder has its own set of options to set the quality-vs-size balance,
464 use the options for the encoder you are using to set the quality level to a
465 point acceptable for your tastes. The most common options to do that are
466 @option{-qscale} and @option{-qmax}, but you should peruse the documentation
467 of the encoder you chose.
471 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
473 Yes. Check the @file{doc/examples} directory in the source
474 repository, also available online at:
475 @url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}.
477 Examples are also installed by default, usually in
478 @code{$PREFIX/share/ffmpeg/examples}.
480 Also you may read the Developers Guide of the FFmpeg documentation. Alternatively,
481 examine the source code for one of the many open source projects that
482 already incorporate FFmpeg at (@url{projects.html}).
484 @section Can you support my C compiler XXX?
486 It depends. If your compiler is C99-compliant, then patches to support
487 it are likely to be welcome if they do not pollute the source code
488 with @code{#ifdef}s related to the compiler.
490 @section Is Microsoft Visual C++ supported?
492 Yes. Please see the @uref{platform.html, Microsoft Visual C++}
493 section in the FFmpeg documentation.
495 @section Can you add automake, libtool or autoconf support?
497 No. These tools are too bloated and they complicate the build.
499 @section Why not rewrite FFmpeg in object-oriented C++?
501 FFmpeg is already organized in a highly modular manner and does not need to
502 be rewritten in a formal object language. Further, many of the developers
503 favor straight C; it works for them. For more arguments on this matter,
504 read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
506 @section Why are the ffmpeg programs devoid of debugging symbols?
508 The build process creates @command{ffmpeg_g}, @command{ffplay_g}, etc. which
509 contain full debug information. Those binaries are stripped to create
510 @command{ffmpeg}, @command{ffplay}, etc. If you need the debug information, use
513 @section I do not like the LGPL, can I contribute code under the GPL instead?
515 Yes, as long as the code is optional and can easily and cleanly be placed
516 under #if CONFIG_GPL without breaking anything. So, for example, a new codec
517 or filter would be OK under GPL while a bug fix to LGPL code would not.
519 @section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves.
521 FFmpeg builds static libraries by default. In static libraries, dependencies
522 are not handled. That has two consequences. First, you must specify the
523 libraries in dependency order: @code{-lavdevice} must come before
524 @code{-lavformat}, @code{-lavutil} must come after everything else, etc.
525 Second, external libraries that are used in FFmpeg have to be specified too.
527 An easy way to get the full list of required libraries in dependency order
528 is to use @code{pkg-config}.
531 c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec)
534 See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for
537 @section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.
539 FFmpeg is a pure C project, so to use the libraries within your C++ application
540 you need to explicitly state that you are using a C library. You can do this by
541 encompassing your FFmpeg includes using @code{extern "C"}.
543 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
545 @section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope
547 FFmpeg is a pure C project using C99 math features, in order to enable C++
548 to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS
550 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
552 You have to create a custom AVIOContext using @code{avio_alloc_context},
553 see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources.
555 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
557 see @url{http://www.ffmpeg.org/~michael/}
559 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
561 Even if peculiar since it is network oriented, RTP is a container like any
562 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
563 In this specific case please look at RFC 4629 to see how it should be done.
565 @section AVStream.r_frame_rate is wrong, it is much larger than the frame rate.
567 @code{r_frame_rate} is NOT the average frame rate, it is the smallest frame rate
568 that can accurately represent all timestamps. So no, it is not
569 wrong if it is larger than the average!
570 For example, if you have mixed 25 and 30 fps content, then @code{r_frame_rate}
571 will be 150 (it is the least common multiple).
572 If you are looking for the average frame rate, see @code{AVStream.avg_frame_rate}.
574 @section Why is @code{make fate} not running all tests?
576 Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable
577 or @code{FATE_SAMPLES} environment variable or the @code{--samples}
578 @command{configure} option is set to the right path.
580 @section Why is @code{make fate} not finding the samples?
582 Do you happen to have a @code{~} character in the samples path to indicate a
583 home directory? The value is used in ways where the shell cannot expand it,
584 causing FATE to not find files. Just replace @code{~} by the full path.