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...
84 @section ffmpeg does not work; what is wrong?
86 Try a @code{make distclean} in the ffmpeg source directory before the build.
87 If this does not help see
88 (@url{http://ffmpeg.org/bugreports.html}).
90 @section How do I encode single pictures into movies?
92 First, rename your pictures to follow a numerical sequence.
93 For example, img1.jpg, img2.jpg, img3.jpg,...
97 ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
100 Notice that @samp{%d} is replaced by the image number.
102 @file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
104 If you have large number of pictures to rename, you can use the
105 following command to ease the burden. The command, using the bourne
106 shell syntax, symbolically links all files in the current directory
107 that match @code{*jpg} to the @file{/tmp} directory in the sequence of
108 @file{img001.jpg}, @file{img002.jpg} and so on.
111 x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
114 If you want to sequence them by oldest modified first, substitute
115 @code{$(ls -r -t *jpg)} in place of @code{*jpg}.
120 ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
123 The same logic is used for any image format that ffmpeg reads.
125 @section How do I encode movie to single pictures?
130 ffmpeg -i movie.mpg movie%d.jpg
133 The @file{movie.mpg} used as input will be converted to
134 @file{movie1.jpg}, @file{movie2.jpg}, etc...
136 Instead of relying on file format self-recognition, you may also use
142 to force the encoding.
144 Applying that to the previous example:
146 ffmpeg -i movie.mpg -f image2 -c:v mjpeg menu%d.jpg
149 Beware that there is no "jpeg" codec. Use "mjpeg" instead.
151 @section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
153 For multithreaded MPEG* encoding, the encoded slices must be independent,
154 otherwise thread n would practically have to wait for n-1 to finish, so it's
155 quite logical that there is a small reduction of quality. This is not a bug.
157 @section How can I read from the standard input or write to the standard output?
159 Use @file{-} as file name.
161 @section -f jpeg doesn't work.
163 Try '-f image2 test%d.jpg'.
165 @section Why can I not change the frame rate?
167 Some codecs, like MPEG-1/2, only allow a small number of fixed frame rates.
168 Choose a different codec with the -c:v command line option.
170 @section How do I encode Xvid or DivX video with ffmpeg?
172 Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
173 standard (note that there are many other coding formats that use this
174 same standard). Thus, use '-c:v mpeg4' to encode in these formats. The
175 default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
176 a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
177 force the fourcc 'xvid' to be stored as the video fourcc rather than the
180 @section Which are good parameters for encoding high quality MPEG-4?
182 '-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2',
183 things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
185 @section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
187 '-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2'
188 but beware the '-g 100' might cause problems with some decoders.
189 Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
191 @section Interlaced video looks very bad when encoded with ffmpeg, what is wrong?
193 You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
194 material, and try '-top 0/1' if the result looks really messed-up.
196 @section How can I read DirectShow files?
198 If you have built FFmpeg with @code{./configure --enable-avisynth}
199 (only possible on MinGW/Cygwin platforms),
200 then you may use any file that DirectShow can read as input.
202 Just create an "input.avs" text file with this single line ...
204 DirectShowSource("C:\path to your file\yourfile.asf")
206 ... and then feed that text file to ffmpeg:
211 For ANY other help on Avisynth, please visit the
212 @uref{http://www.avisynth.org/, Avisynth homepage}.
214 @section How can I join video files?
216 To "join" video files is quite ambiguous. The following list explains the
217 different kinds of "joining" and points out how those are addressed in
218 FFmpeg. To join video files may mean:
223 To put them one after the other: this is called to @emph{concatenate} them
224 (in short: concat) and is addressed
225 @ref{How can I concatenate video files, in this very faq}.
228 To put them together in the same file, to let the user choose between the
229 different versions (example: different audio languages): this is called to
230 @emph{multiplex} them together (in short: mux), and is done by simply
231 invoking ffmpeg with several @option{-i} options.
234 For audio, to put all channels together in a single stream (example: two
235 mono streams into one stereo stream): this is sometimes called to
236 @emph{merge} them, and can be done using the
237 @url{http://ffmpeg.org/ffmpeg.html#amerge, @code{amerge}} filter.
240 For audio, to play one on top of the other: this is called to @emph{mix}
241 them, and can be done by first merging them into a single stream and then
242 using the @url{http://ffmpeg.org/ffmpeg.html#pan, @code{pan}} filter to mix
243 the channels at will.
246 For video, to display both together, side by side or one on top of a part of
247 the other; it can be done using the
248 @url{http://ffmpeg.org/ffmpeg.html#overlay, @code{overlay}} video filter.
252 @anchor{How can I concatenate video files}
253 @section How can I concatenate video files?
255 There are several solutions, depending on the exact circumstances.
257 @subsection Concatenating using filters
259 FFmpeg has a @url{http://ffmpeg.org/ffmpeg.html#concat-1, @code{concat}}
260 filter designed specifically for that, with examples in the documentation.
262 @subsection Concatenating at the file level
264 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to concatenate
265 video by merely concatenating the files them.
267 Hence you may concatenate your multimedia files by first transcoding them to
268 these privileged formats, then using the humble @code{cat} command (or the
269 equally humble @code{copy} under Windows), and finally transcoding back to your
273 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
274 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
275 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
276 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
279 Additionally, you can use the @code{concat} protocol instead of @code{cat} or
280 @code{copy} which will avoid creation of a potentially huge intermediate file.
283 ffmpeg -i input1.avi -qscale:v 1 intermediate1.mpg
284 ffmpeg -i input2.avi -qscale:v 1 intermediate2.mpg
285 ffmpeg -i concat:"intermediate1.mpg|intermediate2.mpg" -c copy intermediate_all.mpg
286 ffmpeg -i intermediate_all.mpg -qscale:v 2 output.avi
289 Note that you may need to escape the character "|" which is special for many
292 Another option is usage of named pipes, should your platform support it:
295 mkfifo intermediate1.mpg
296 mkfifo intermediate2.mpg
297 ffmpeg -i input1.avi -qscale:v 1 -y intermediate1.mpg < /dev/null &
298 ffmpeg -i input2.avi -qscale:v 1 -y intermediate2.mpg < /dev/null &
299 cat intermediate1.mpg intermediate2.mpg |\
300 ffmpeg -f mpeg -i - -c:v mpeg4 -acodec libmp3lame output.avi
303 @subsection Concatenating using raw audio and video
305 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
306 allow concatenation, and the transcoding step is almost lossless.
307 When using multiple yuv4mpegpipe(s), the first line needs to be discarded
308 from all but the first stream. This can be accomplished by piping through
309 @code{tail} as seen below. Note that when piping through @code{tail} you
310 must use command grouping, @code{@{ ;@}}, to background properly.
312 For example, let's say we want to concatenate two FLV files into an
322 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
323 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
324 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
325 @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
326 cat temp1.a temp2.a > all.a &
327 cat temp1.v temp2.v > all.v &
328 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
329 -f yuv4mpegpipe -i all.v \
331 rm temp[12].[av] all.[av]
334 @section -profile option fails when encoding H.264 video with AAC audio
336 @command{ffmpeg} prints an error like
339 Undefined constant or missing '(' in 'baseline'
340 Unable to parse option value "baseline"
341 Error setting option profile to value baseline.
344 Short answer: write @option{-profile:v} instead of @option{-profile}.
346 Long answer: this happens because the @option{-profile} option can apply to both
347 video and audio. Specifically the AAC encoder also defines some profiles, none
348 of which are named @var{baseline}.
350 The solution is to apply the @option{-profile} option to the video stream only
351 by using @url{http://ffmpeg.org/ffmpeg.html#Stream-specifiers-1, Stream specifiers}.
352 Appending @code{:v} to it will do exactly that.
354 @section Using @option{-f lavfi}, audio becomes mono for no apparent reason.
356 Use @option{-dumpgraph -} to find out exactly where the channel layout is
359 Most likely, it is through @code{auto-inserted aconvert}. Try to understand
360 why the converting filter was needed at that place.
362 Just before the output is a likely place, as @option{-f lavfi} currently
363 only support packed S16.
365 Then insert the correct @code{aconvert} explicitly in the filter graph,
366 specifying the exact format.
369 aconvert=s16:stereo:packed
372 @section Why does FFmpeg not see the subtitles in my VOB file?
374 VOB and a few other formats do not have a global header that describes
375 everything present in the file. Instead, applications are supposed to scan
376 the file to see what it contains. Since VOB files are frequently large, only
377 the beginning is scanned. If the subtitles happen only later in the file,
378 they will not be initally detected.
380 Some applications, including the @code{ffmpeg} command-line tool, can only
381 work with streams that were detected during the initial scan; streams that
382 are detected later are ignored.
384 The size of the initial scan is controlled by two options: @code{probesize}
385 (default ~5 Mo) and @code{analyzeduration} (default 5,000,000 µs = 5 s). For
386 the subtitle stream to be detected, both values must be large enough.
390 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
392 Yes. Check the @file{doc/examples} directory in the source
393 repository, also available online at:
394 @url{https://github.com/FFmpeg/FFmpeg/tree/master/doc/examples}.
396 Examples are also installed by default, usually in
397 @code{$PREFIX/share/ffmpeg/examples}.
399 Also you may read the Developers Guide of the FFmpeg documentation. Alternatively,
400 examine the source code for one of the many open source projects that
401 already incorporate FFmpeg at (@url{projects.html}).
403 @section Can you support my C compiler XXX?
405 It depends. If your compiler is C99-compliant, then patches to support
406 it are likely to be welcome if they do not pollute the source code
407 with @code{#ifdef}s related to the compiler.
409 @section Is Microsoft Visual C++ supported?
411 Yes. Please see the @uref{platform.html, Microsoft Visual C++}
412 section in the FFmpeg documentation.
414 @section Can you add automake, libtool or autoconf support?
416 No. These tools are too bloated and they complicate the build.
418 @section Why not rewrite FFmpeg in object-oriented C++?
420 FFmpeg is already organized in a highly modular manner and does not need to
421 be rewritten in a formal object language. Further, many of the developers
422 favor straight C; it works for them. For more arguments on this matter,
423 read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
425 @section Why are the ffmpeg programs devoid of debugging symbols?
427 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
428 information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
429 you need the debug information, use the *_g versions.
431 @section I do not like the LGPL, can I contribute code under the GPL instead?
433 Yes, as long as the code is optional and can easily and cleanly be placed
434 under #if CONFIG_GPL without breaking anything. So, for example, a new codec
435 or filter would be OK under GPL while a bug fix to LGPL code would not.
437 @section I'm using FFmpeg from within my C application but the linker complains about missing symbols from the libraries themselves.
439 FFmpeg builds static libraries by default. In static libraries, dependencies
440 are not handled. That has two consequences. First, you must specify the
441 libraries in dependency order: @code{-lavdevice} must come before
442 @code{-lavformat}, @code{-lavutil} must come after everything else, etc.
443 Second, external libraries that are used in FFmpeg have to be specified too.
445 An easy way to get the full list of required libraries in dependency order
446 is to use @code{pkg-config}.
449 c99 -o program program.c $(pkg-config --cflags --libs libavformat libavcodec)
452 See @file{doc/example/Makefile} and @file{doc/example/pc-uninstalled} for
455 @section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.
457 FFmpeg is a pure C project, so to use the libraries within your C++ application
458 you need to explicitly state that you are using a C library. You can do this by
459 encompassing your FFmpeg includes using @code{extern "C"}.
461 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
463 @section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope
465 FFmpeg is a pure C project using C99 math features, in order to enable C++
466 to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS
468 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
470 You have to create a custom AVIOContext using @code{avio_alloc_context},
471 see @file{libavformat/aviobuf.c} in FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer or MPlayer2 sources.
473 @section Where can I find libav* headers for Pascal/Delphi?
475 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
477 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
479 see @url{http://www.ffmpeg.org/~michael/}
481 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
483 Even if peculiar since it is network oriented, RTP is a container like any
484 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
485 In this specific case please look at RFC 4629 to see how it should be done.
487 @section AVStream.r_frame_rate is wrong, it is much larger than the frame rate.
489 r_frame_rate is NOT the average frame rate, it is the smallest frame rate
490 that can accurately represent all timestamps. So no, it is not
491 wrong if it is larger than the average!
492 For example, if you have mixed 25 and 30 fps content, then r_frame_rate
495 @section Why is @code{make fate} not running all tests?
497 Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable
498 or @code{FATE_SAMPLES} environment variable or the @code{--samples}
499 @command{configure} option is set to the right path.
501 @section Why is @code{make fate} not finding the samples?
503 Do you happen to have a @code{~} character in the samples path to indicate a
504 home directory? The value is used in ways where the shell cannot expand it,
505 causing FATE to not find files. Just replace @code{~} by the full path.