faq.texi 18.2 KB
Newer Older
1 2
\input texinfo @c -*- texinfo -*-

3
@settitle FFmpeg FAQ
4
@titlepage
5
@center @titlefont{FFmpeg FAQ}
6 7
@end titlepage

8 9 10
@top

@contents
11

12 13
@chapter General Questions

14
@section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
15

16
Like most open source projects FFmpeg suffers from a certain lack of
17 18 19 20 21 22
manpower. For this reason the developers have to prioritize the work
they do and putting out releases is not at the top of the list, fixing
bugs and reviewing patches takes precedence. Please don't complain or
request more timely and/or frequent releases unless you are willing to
help out creating them.

23 24
@section I have a problem with an old version of FFmpeg; where should I report it?
Nowhere. We do not support old FFmpeg versions in any way, we simply lack
25
the time, motivation and manpower to do so. If you have a problem with an
26
old version of FFmpeg, upgrade to the latest git snapshot. If you
27 28
still experience the problem, then you can report it according to the
guidelines in @url{http://ffmpeg.org/bugreports.html}.
29

30
@section Why doesn't FFmpeg support feature [xyz]?
31

32
Because no one has taken on that task yet. FFmpeg development is
33 34
driven by the tasks that are important to the individual developers.
If there is a feature that is important to you, the best way to get
35
it implemented is to undertake the task yourself or sponsor a developer.
36

37
@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?
38

39
No. Windows DLLs are not portable, bloated and often slow.
40
Moreover FFmpeg strives to support all codecs natively.
41
A DLL loader is not conducive to that goal.
42

43
@section My bug report/mail to ffmpeg-devel/user has not received any replies.
44 45 46 47 48

Likely reasons
@itemize
@item We are busy and haven't had time yet to read your report or
investigate the issue.
49
@item You didn't follow @url{http://ffmpeg.org/bugreports.html}.
50
@item You didn't use git HEAD.
51 52 53 54 55 56 57
@item You reported a segmentation fault without gdb output.
@item You describe a problem but not how to reproduce it.
@item It's unclear if you use ffmpeg as command line tool or use
libav* from another application.
@item You speak about a video having problems on playback but
not what you use to play it.
@item We have no faint clue what you are talking about besides
58
that it is related to FFmpeg.
59 60
@end itemize

61
@section Is there a forum for FFmpeg? I do not like mailing lists.
62

Víctor Paesa's avatar
Víctor Paesa committed
63 64
You may view our mailing lists with a more forum-alike look here:
@url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user},
Víctor Paesa's avatar
Víctor Paesa committed
65
but, if you post, please remember that our mailing list rules still apply there.
66

Mike Melanson's avatar
Mike Melanson committed
67
@section I cannot read this file although this format seems to be supported by ffmpeg.
68

69
Even if ffmpeg can read the container format, it may not support all its
70 71 72
codecs. Please consult the supported codec list in the ffmpeg
documentation.

73 74 75
@section Which codecs are supported by Windows?

Windows does not support standard formats like MPEG very well, unless you
76
install some additional codecs.
77 78 79 80 81 82 83 84 85 86 87 88

The following list of video codecs should work on most Windows systems:
@table @option
@item msmpeg4v2
.avi/.asf
@item msmpeg4
.asf only
@item wmv1
.asf only
@item wmv2
.asf only
@item mpeg4
89
Only if you have some MPEG-4 codec like ffdshow or Xvid installed.
90
@item mpeg1video
91 92 93 94 95 96 97 98 99 100 101
.mpg only
@end table
Note, ASF files often have .wmv or .wma extensions in Windows. It should also
be mentioned that Microsoft claims a patent on the ASF format, and may sue
or threaten users who create ASF files with non-Microsoft software. It is
strongly advised to avoid ASF where possible.

The following list of audio codecs should work on most Windows systems:
@table @option
@item adpcm_ima_wav
@item adpcm_ms
102
@item pcm_s16le
103
always
104
@item libmp3lame
105
If some MP3 codec like LAME is installed.
106 107 108
@end table


109 110 111 112 113 114 115
@chapter Compilation

@section @code{error: can't find a register in class 'GENERAL_REGS' while reloading 'asm'}

This is a bug in gcc. Do not report it to us. Instead, please report it to
the gcc developers. Note that we will not add workarounds for gcc bugs.

116 117 118 119 120
Also note that (some of) the gcc developers believe this is not a bug or
not a bug they should fix:
@url{http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11203}.
Then again, some of them do not know the difference between an undecidable
problem and an NP-hard problem...
121

122 123
@chapter Usage

124
@section ffmpeg does not work; what is wrong?
125

126
Try a @code{make distclean} in the ffmpeg source directory before the build. If this does not help see
127 128
(@url{http://ffmpeg.org/bugreports.html}).

129
@section How do I encode single pictures into movies?
130

Víctor Paesa's avatar
Víctor Paesa committed
131 132 133
First, rename your pictures to follow a numerical sequence.
For example, img1.jpg, img2.jpg, img3.jpg,...
Then you may run:
134 135

@example
136
  ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
137 138
@end example

Víctor Paesa's avatar
Víctor Paesa committed
139
Notice that @samp{%d} is replaced by the image number.
140

Víctor Paesa's avatar
Víctor Paesa committed
141
@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
142

143 144 145 146 147 148 149
If you have large number of pictures to rename, you can use the
following command to ease the burden. The command, using the bourne
shell syntax, symbolically links all files in the current directory
that match @code{*jpg} to the @file{/tmp} directory in the sequence of
@file{img001.jpg}, @file{img002.jpg} and so on.

@example
150
  x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done
151 152 153 154 155 156 157 158 159 160 161
@end example

If you want to sequence them by oldest modified first, substitute
@code{$(ls -r -t *jpg)} in place of @code{*jpg}.

Then run:

@example
  ffmpeg -f image2 -i /tmp/img%03d.jpg /tmp/a.mpg
@end example

Víctor Paesa's avatar
Víctor Paesa committed
162
The same logic is used for any image format that ffmpeg reads.
163

164
@section How do I encode movie to single pictures?
165

166
Use:
167 168

@example
169
  ffmpeg -i movie.mpg movie%d.jpg
170 171
@end example

172 173
The @file{movie.mpg} used as input will be converted to
@file{movie1.jpg}, @file{movie2.jpg}, etc...
174 175 176 177 178 179 180 181 182 183 184

Instead of relying on file format self-recognition, you may also use
@table @option
@item -vcodec ppm
@item -vcodec png
@item -vcodec mjpeg
@end table
to force the encoding.

Applying that to the previous example:
@example
185
  ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
186 187 188 189
@end example

Beware that there is no "jpeg" codec. Use "mjpeg" instead.

190
@section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
191 192

For multithreaded MPEG* encoding, the encoded slices must be independent,
Mike Melanson's avatar
Mike Melanson committed
193 194
otherwise thread n would practically have to wait for n-1 to finish, so it's
quite logical that there is a small reduction of quality. This is not a bug.
195

196
@section How can I read from the standard input or write to the standard output?
Fabrice Bellard's avatar
Fabrice Bellard committed
197

198
Use @file{-} as file name.
Fabrice Bellard's avatar
Fabrice Bellard committed
199

200
@section -f jpeg doesn't work.
Michael Niedermayer's avatar
Michael Niedermayer committed
201

202
Try '-f image2 test%d.jpg'.
Michael Niedermayer's avatar
Michael Niedermayer committed
203

Mike Melanson's avatar
Mike Melanson committed
204
@section Why can I not change the framerate?
Michael Niedermayer's avatar
Michael Niedermayer committed
205

206
Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
Mike Melanson's avatar
Mike Melanson committed
207
Choose a different codec with the -vcodec command line option.
Michael Niedermayer's avatar
Michael Niedermayer committed
208

209
@section How do I encode Xvid or DivX video with ffmpeg?
210

211
Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4
212
standard (note that there are many other coding formats that use this
213
same standard). Thus, use '-vcodec mpeg4' to encode in these formats. The
214
default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
215 216
a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
force the fourcc 'xvid' to be stored as the video fourcc rather than the
217 218
default.

Diego Biurrun's avatar
Diego Biurrun committed
219
@section How do I encode videos which play on the iPod?
220 221

@table @option
Diego Biurrun's avatar
Diego Biurrun committed
222
@item needed stuff
223
-acodec libfaac -vcodec mpeg4 width<=320 height<=240
Diego Biurrun's avatar
Diego Biurrun committed
224
@item working stuff
225
mv4, title
Diego Biurrun's avatar
Diego Biurrun committed
226 227
@item non-working stuff
B-frames
228
@item example command line
229
ffmpeg -i input -acodec libfaac -ab 128k -vcodec mpeg4 -b 1200k -mbd 2 -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -s 320x180 -metadata title=X output.mp4
230 231
@end table

Diego Biurrun's avatar
Diego Biurrun committed
232
@section How do I encode videos which play on the PSP?
233 234

@table @option
Diego Biurrun's avatar
Diego Biurrun committed
235
@item needed stuff
236
-acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
Diego Biurrun's avatar
Diego Biurrun committed
237
@item working stuff
238
mv4, title
Diego Biurrun's avatar
Diego Biurrun committed
239 240
@item non-working stuff
B-frames
241
@item example command line
242
ffmpeg -i input -acodec libfaac -ab 128k -vcodec mpeg4 -b 1200k -ar 24000 -mbd 2 -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -metadata title=X -f psp output.mp4
243
@item needed stuff for H.264
244
-acodec libfaac -vcodec libx264 width*height<=76800 width%16=0? height%16=0? -ar 48000 -coder 1 -r 30000/1001 or 15000/1001 -f psp
245 246 247 248 249
@item working stuff for H.264
title, loop filter
@item non-working stuff for H.264
CAVLC
@item example command line
250
ffmpeg -i input -acodec libfaac -ab 128k -vcodec libx264 -b 1200k -ar 48000 -mbd 2 -coder 1 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -metadata title=X -f psp -flags loop -trellis 2 -partitions parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 output.mp4
251 252 253
@item higher resolution for newer PSP firmwares, width<=480, height<=272
-vcodec libx264 -level 21 -coder 1 -f psp
@item example command line
254
ffmpeg -i input -acodec libfaac -ab 128k -ac 2 -ar 48000 -vcodec libx264 -level 21 -b 640k -coder 1 -f psp -flags +loop -trellis 2 -partitions +parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 -g 250 -s 480x272 output.mp4
255 256
@end table

Diego Biurrun's avatar
Diego Biurrun committed
257
@section Which are good parameters for encoding high quality MPEG-4?
258

259
'-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2',
Diego Biurrun's avatar
Diego Biurrun committed
260
things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
261

Diego Biurrun's avatar
Diego Biurrun committed
262
@section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
263

264
'-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2'
Diego Biurrun's avatar
Diego Biurrun committed
265 266
but beware the '-g 100' might cause problems with some decoders.
Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
267

Diego Biurrun's avatar
Diego Biurrun committed
268
@section Interlaced video looks very bad when encoded with ffmpeg, what is wrong?
269

Diego Biurrun's avatar
Diego Biurrun committed
270 271
You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
material, and try '-top 0/1' if the result looks really messed-up.
272

Diego Biurrun's avatar
Diego Biurrun committed
273
@section How can I read DirectShow files?
274

275
If you have built FFmpeg with @code{./configure --enable-avisynth}
Diego Biurrun's avatar
Diego Biurrun committed
276 277
(only possible on MinGW/Cygwin platforms),
then you may use any file that DirectShow can read as input.
278 279 280 281 282

Just create an "input.avs" text file with this single line ...
@example
  DirectShowSource("C:\path to your file\yourfile.asf")
@end example
283
... and then feed that text file to ffmpeg:
284 285 286 287 288 289
@example
  ffmpeg -i input.avs
@end example

For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.

290 291
@section How can I join video files?

292
A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
293 294 295 296
merely concatenating them.

Hence you may concatenate your multimedia files by first transcoding them to
these privileged formats, then using the humble @code{cat} command (or the
297
equally humble @code{copy} under Windows), and finally transcoding back to your
298 299 300 301 302 303 304 305 306 307 308 309 310
format of choice.

@example
ffmpeg -i input1.avi -sameq intermediate1.mpg
ffmpeg -i input2.avi -sameq intermediate2.mpg
cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
ffmpeg -i intermediate_all.mpg -sameq output.avi
@end example

Notice that you should either use @code{-sameq} or set a reasonably high
bitrate for your intermediate and output files, if you want to preserve
video quality.

311
Also notice that you may avoid the huge intermediate files by taking advantage
312 313 314 315 316 317 318 319
of named pipes, should your platform support it:

@example
mkfifo intermediate1.mpg
mkfifo intermediate2.mpg
ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null &
ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null &
cat intermediate1.mpg intermediate2.mpg |\
320
ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi
321 322 323 324
@end example

Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
allow concatenation, and the transcoding step is almost lossless.
325 326 327 328 329
When using multiple yuv4mpegpipe(s), the first line needs to be discarded
from all but the first stream. This can be accomplished by piping through
@code{tail} as seen below. Note that when piping through @code{tail} you
must use command grouping, @code{@{  ;@}}, to background properly.

330 331 332 333 334 335 336 337 338 339 340 341
For example, let's say we want to join two FLV files into an output.flv file:

@example
mkfifo temp1.a
mkfifo temp1.v
mkfifo temp2.a
mkfifo temp2.v
mkfifo all.a
mkfifo all.v
ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
342
@{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} &
343 344 345 346 347 348 349 350
cat temp1.a temp2.a > all.a &
cat temp1.v temp2.v > all.v &
ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
       -f yuv4mpegpipe -i all.v \
       -sameq -y output.flv
rm temp[12].[av] all.[av]
@end example

351
@section The ffmpeg program does not respect the -maxrate setting, some frames are bigger than maxrate/fps.
352

Diego Biurrun's avatar
Diego Biurrun committed
353
Read the MPEG spec about video buffer verifier.
354

Diego Biurrun's avatar
Diego Biurrun committed
355
@section I want CBR, but no matter what I do frame sizes differ.
356

Diego Biurrun's avatar
Diego Biurrun committed
357 358 359
You do not understand what CBR is, please read the MPEG spec.
Read about video buffer verifier and constant bitrate.
The one sentence summary is that there is a buffer and the input rate is
360 361
constant, the output can vary as needed.

Diego Biurrun's avatar
Diego Biurrun committed
362
@section How do I check if a stream is CBR?
363 364 365 366 367

To quote the MPEG-2 spec:
"There is no way to tell that a bitstream is constant bitrate without
examining all of the vbv_delay values and making complicated computations."

Michael Niedermayer's avatar
Michael Niedermayer committed
368

369 370
@chapter Development

371
@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
372

373
Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
374
examine the source code for one of the many open source projects that
375
already incorporate FFmpeg at (@url{projects.html}).
376

377
@section Can you support my C compiler XXX?
378

Diego Biurrun's avatar
Diego Biurrun committed
379 380 381
It depends. If your compiler is C99-compliant, then patches to support
it are likely to be welcome if they do not pollute the source code
with @code{#ifdef}s related to the compiler.
382

383
@section Is Microsoft Visual C++ supported?
384

385
No. Microsoft Visual C++ is not compliant to the C99 standard and does
386
not - among other things - support the inline assembly used in FFmpeg.
387
If you wish to use MSVC++ for your
388
project then you can link the MSVC++ code with libav* as long as
389
you compile the latter with a working C compiler. For more information, see
390
the @emph{Microsoft Visual C++ compatibility} section in the FFmpeg
391
documentation.
392

393
There have been efforts to make FFmpeg compatible with MSVC++ in the
394
past. However, they have all been rejected as too intrusive, especially
395
since MinGW does the job adequately. None of the core developers
396
work with MSVC++ and thus this item is low priority. Should you find
397 398
the silver bullet that solves this problem, feel free to shoot it at us.

399 400
We strongly recommend you to move over from MSVC++ to MinGW tools.

401
@section Can I use FFmpeg or libavcodec under Windows?
402

403 404
Yes, but the Cygwin or MinGW tools @emph{must} be used to compile FFmpeg.
Read the @emph{Windows} section in the FFmpeg documentation to find more
405
information.
406

407
To get help and instructions for building FFmpeg under Windows, check out
408
the FFmpeg Windows Help Forum at
409
@url{http://ffmpeg.arrozcru.org/}.
410

411
@section Can you add automake, libtool or autoconf support?
412

Diego Biurrun's avatar
Diego Biurrun committed
413
No. These tools are too bloated and they complicate the build.
414

415
@section Why not rewrite ffmpeg in object-oriented C++?
416

417
FFmpeg is already organized in a highly modular manner and does not need to
418
be rewritten in a formal object language. Further, many of the developers
Mike Melanson's avatar
Mike Melanson committed
419
favor straight C; it works for them. For more arguments on this matter,
420
read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
Mike Melanson's avatar
Mike Melanson committed
421

422
@section Why are the ffmpeg programs devoid of debugging symbols?
Mike Melanson's avatar
Mike Melanson committed
423 424

The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
425
information. Those binaries are stripped to create ffmpeg, ffplay, etc. If
Tilman Brock's avatar
Tilman Brock committed
426
you need the debug information, use the *_g versions.
427

428
@section I do not like the LGPL, can I contribute code under the GPL instead?
429

Diego Biurrun's avatar
Diego Biurrun committed
430
Yes, as long as the code is optional and can easily and cleanly be placed
431
under #if CONFIG_GPL without breaking anything. So for example a new codec
432
or filter would be OK under GPL while a bug fix to LGPL code would not.
433

Diego Biurrun's avatar
Diego Biurrun committed
434
@section I want to compile xyz.c alone but my compiler produced many errors.
435

Diego Biurrun's avatar
Diego Biurrun committed
436 437 438 439 440
Common code is in its own files in libav* and is used by the individual
codecs. They will not work without the common parts, you have to compile
the whole libav*. If you wish, disable some parts with configure switches.
You can also try to hack it and remove more, but if you had problems fixing
the compilation failure then you are probably not qualified for this.
441

442 443
@section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available.

444
FFmpeg is a pure C project, so to use the libraries within your C++ application
445
you need to explicitly state that you are using a C library. You can do this by
446
encompassing your FFmpeg includes using @code{extern "C"}.
447 448 449

See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3}

Diego Biurrun's avatar
Diego Biurrun committed
450
@section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat?
Michael Niedermayer's avatar
Michael Niedermayer committed
451

452
You have to implement a URLProtocol, see @file{libavformat/file.c} in
453
FFmpeg and @file{libmpdemux/demux_lavf.c} in MPlayer sources.
Michael Niedermayer's avatar
Michael Niedermayer committed
454

Ramiro Polla's avatar
Ramiro Polla committed
455 456 457 458
@section I get "No compatible shell script interpreter found." in MSys.

The standard MSys bash (2.04) is broken. You need to install 2.05 or later.

459 460 461 462
@section I get "./configure: line <xxx>: pr: command not found" in MSys.

The standard MSys install doesn't come with pr. You need to get it from the coreutils package.

Diego Biurrun's avatar
Diego Biurrun committed
463
@section Where can I find libav* headers for Pascal/Delphi?
464 465 466

see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}

Diego Biurrun's avatar
Diego Biurrun committed
467
@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
468

469
see @url{http://www.ffmpeg.org/~michael/}
470

471
@section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
Michael Niedermayer's avatar
Michael Niedermayer committed
472

Luca Barbato's avatar
Luca Barbato committed
473
Even if peculiar since it is network oriented, RTP is a container like any
474 475
other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
In this specific case please look at RFC 4629 to see how it should be done.
Michael Niedermayer's avatar
Michael Niedermayer committed
476

477
@section AVStream.r_frame_rate is wrong, it is much larger than the framerate.
Michael Niedermayer's avatar
Michael Niedermayer committed
478 479

r_frame_rate is NOT the average framerate, it is the smallest framerate
480 481 482
that can accurately represent all timestamps. So no, it is not
wrong if it is larger than the average!
For example, if you have mixed 25 and 30 fps content, then r_frame_rate
Michael Niedermayer's avatar
Michael Niedermayer committed
483 484
will be 150.

485
@bye