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 A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
217 merely concatenating them.
219 Hence you may concatenate your multimedia files by first transcoding them to
220 these privileged formats, then using the humble @code{cat} command (or the
221 equally humble @code{copy} under Windows), and finally transcoding back to your
225 ffmpeg -i input1.avi -same_quant intermediate1.mpg
226 ffmpeg -i input2.avi -same_quant intermediate2.mpg
227 cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
228 ffmpeg -i intermediate_all.mpg -same_quant output.avi
231 Notice that you should either use @code{-same_quant} or set a reasonably high
232 bitrate for your intermediate and output files, if you want to preserve
235 Also notice that you may avoid the huge intermediate files by taking advantage
236 of named pipes, should your platform support it:
239 mkfifo intermediate1.mpg
240 mkfifo intermediate2.mpg
241 ffmpeg -i input1.avi -same_quant -y intermediate1.mpg < /dev/null &
242 ffmpeg -i input2.avi -same_quant -y intermediate2.mpg < /dev/null &
243 cat intermediate1.mpg intermediate2.mpg |\
244 ffmpeg -f mpeg -i - -same_quant -c:v mpeg4 -acodec libmp3lame output.avi
247 Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
248 allow concatenation, and the transcoding step is almost lossless.
249 When using multiple yuv4mpegpipe(s), the first line needs to be discarded
250 from all but the first stream. This can be accomplished by piping through
251 @code{tail} as seen below. Note that when piping through @code{tail} you
252 must use command grouping, @code{@{ ;@}}, to background properly.
254 For example, let's say we want to join two FLV files into an output.flv file:
263 ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
264 ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
265 ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
266 @{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
267 cat temp1.a temp2.a > all.a &
268 cat temp1.v temp2.v > all.v &
269 ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
270 -f yuv4mpegpipe -i all.v \
271 -same_quant -y output.flv
272 rm temp[12].[av] all.[av]
275 @section -profile option fails when encoding H.264 video with AAC audio
277 @command{ffmpeg} prints an error like
280 Undefined constant or missing '(' in 'baseline'
281 Unable to parse option value "baseline"
282 Error setting option profile to value baseline.
285 Short answer: write @option{-profile:v} instead of @option{-profile}.
287 Long answer: this happens because the @option{-profile} option can apply to both
288 video and audio. Specifically the AAC encoder also defines some profiles, none
289 of which are named @var{baseline}.
291 The solution is to apply the @option{-profile} option to the video stream only
292 by using @url{http://ffmpeg.org/ffmpeg.html#Stream-specifiers-1, Stream specifiers}.
293 Appending @code{:v} to it will do exactly that.
295 @section Using @option{-f lavfi}, audio becomes mono for no apparent reason.
297 Use @option{-dumpgraph -} to find out exactly where the channel layout is
300 Most likely, it is through @code{auto-inserted aconvert}. Try to understand
301 why the converting filter was needed at that place.
303 Just before the output is a likely place, as @option{-f lavfi} currently
304 only support packed S16.
306 Then insert the correct @code{aconvert} explicitly in the filter graph,
307 specifying the exact format.
310 aconvert=s16:stereo:packed
315 @section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
317 Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
318 examine the source code for one of the many open source projects that
319 already incorporate FFmpeg at (@url{projects.html}).
321 @section Can you support my C compiler XXX?
323 It depends. If your compiler is C99-compliant, then patches to support
324 it are likely to be welcome if they do not pollute the source code
325 with @code{#ifdef}s related to the compiler.
327 @section Is Microsoft Visual C++ supported?
329 No. Microsoft Visual C++ is not compliant to the C99 standard and does
330 not - among other things - support the inline assembly used in FFmpeg.
331 If you wish to use MSVC++ for your
332 project then you can link the MSVC++ code with libav* as long as
333 you compile the latter with a working C compiler. For more information, see
334 the @emph{Microsoft Visual C++ compatibility} section in the FFmpeg
337 There have been efforts to make FFmpeg compatible with MSVC++ in the
338 past. However, they have all been rejected as too intrusive, especially
339 since MinGW does the job adequately. None of the core developers
340 work with MSVC++ and thus this item is low priority. Should you find
341 the silver bullet that solves this problem, feel free to shoot it at us.
343 We strongly recommend you to move over from MSVC++ to MinGW tools.
345 @section Can I use FFmpeg or libavcodec under Windows?
347 Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg.
348 Read the @emph{Windows} section in the FFmpeg documentation to find more
351 To get help and instructions for building FFmpeg under Windows, check out
352 the FFmpeg Windows Help Forum at
353 @url{http://ffmpeg.arrozcru.org/}.
355 @section Can you add automake, libtool or autoconf support?
357 No. These tools are too bloated and they complicate the build.
359 @section Why not rewrite FFmpeg in object-oriented C++?
361 FFmpeg is already organized in a highly modular manner and does not need to
362 be rewritten in a formal object language. Further, many of the developers
363 favor straight C; it works for them. For more arguments on this matter,
364 read @uref{http://www.tux.org/lkml/#s15, "Programming Religion"}.
366 @section Why are the ffmpeg programs devoid of debugging symbols?
368 The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
369 information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
370 you need the debug information, use the *_g versions.
372 @section I do not like the LGPL, can I contribute code under the GPL instead?
374 Yes, as long as the code is optional and can easily and cleanly be placed
375 under #if CONFIG_GPL without breaking anything. So, for example, a new codec
376 or filter would be OK under GPL while a bug fix to LGPL code would not.
378 @section I'm using FFmpeg from within my C++ application but the linker complains about missing symbols which seem to be available.
380 FFmpeg is a pure C project, so to use the libraries within your C++ application
381 you need to explicitly state that you are using a C library. You can do this by
382 encompassing your FFmpeg includes using @code{extern "C"}.
384 See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}
386 @section I'm using libavutil from within my C++ application but the compiler complains about 'UINT64_C' was not declared in this scope
388 FFmpeg is a pure C project using C99 math features, in order to enable C++
389 to use them you have to append -D__STDC_CONSTANT_MACROS to your CXXFLAGS
391 @section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
393 You have to implement a URLProtocol, see @file{libavformat/file.c} in
394 FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer sources.
396 @section Where can I find libav* headers for Pascal/Delphi?
398 see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
400 @section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
402 see @url{http://www.ffmpeg.org/~michael/}
404 @section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
406 Even if peculiar since it is network oriented, RTP is a container like any
407 other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
408 In this specific case please look at RFC 4629 to see how it should be done.
410 @section AVStream.r_frame_rate is wrong, it is much larger than the frame rate.
412 r_frame_rate is NOT the average frame rate, it is the smallest frame rate
413 that can accurately represent all timestamps. So no, it is not
414 wrong if it is larger than the average!
415 For example, if you have mixed 25 and 30 fps content, then r_frame_rate
418 @section Why is @code{make fate} not running all tests?
420 Make sure you have the fate-suite samples and the @code{SAMPLES} Make variable
421 or @code{FATE_SAMPLES} environment variable or the @code{--samples}
422 @command{configure} option is set to the right path.
424 @section Why is @code{make fate} not finding the samples?
426 Do you happen to have a @code{~} character in the samples path to indicate a
427 home directory? The value is used in ways where the shell cannot expand it,
428 causing FATE to not find files. Just replace @code{~} by the full path.