mirror of https://github.com/FFmpeg/FFmpeg.git
You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
481 lines
18 KiB
481 lines
18 KiB
\input texinfo @c -*- texinfo -*- |
|
|
|
@settitle Libav FAQ |
|
@titlepage |
|
@center @titlefont{Libav FAQ} |
|
@end titlepage |
|
|
|
@top |
|
|
|
@contents |
|
|
|
@chapter General Questions |
|
|
|
@section When will the next Libav version be released? / Why are Libav releases so few and far between? |
|
|
|
Like most open source projects Libav suffers from a certain lack of |
|
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. |
|
|
|
@section I have a problem with an old version of Libav; where should I report it? |
|
Nowhere. We do not support old Libav versions in any way, we simply lack |
|
the time, motivation and manpower to do so. If you have a problem with an |
|
old version of Libav, upgrade to the latest git snapshot. If you |
|
still experience the problem, then you can report it according to the |
|
guidelines in @url{http://libav.org/bugreports.html}. |
|
|
|
@section Why doesn't Libav support feature [xyz]? |
|
|
|
Because no one has taken on that task yet. Libav development is |
|
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 |
|
it implemented is to undertake the task yourself or sponsor a developer. |
|
|
|
@section Libav does not support codec XXX. Can you include a Windows DLL loader to support it? |
|
|
|
No. Windows DLLs are not portable, bloated and often slow. |
|
Moreover Libav strives to support all codecs natively. |
|
A DLL loader is not conducive to that goal. |
|
|
|
@section My bug report/mail to libav-devel/user has not received any replies. |
|
|
|
Likely reasons |
|
@itemize |
|
@item We are busy and haven't had time yet to read your report or |
|
investigate the issue. |
|
@item You didn't follow @url{http://libav.org/bugreports.html}. |
|
@item You didn't use git master. |
|
@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 |
|
that it is related to Libav. |
|
@end itemize |
|
|
|
@section Is there a forum for Libav? I do not like mailing lists. |
|
|
|
You may view our mailing lists with a more forum-alike look here: |
|
@url{http://dir.gmane.org/gmane.comp.video.ffmpeg.user}, |
|
but, if you post, please remember that our mailing list rules still apply there. |
|
|
|
@section I cannot read this file although this format seems to be supported by ffmpeg. |
|
|
|
Even if ffmpeg can read the container format, it may not support all its |
|
codecs. Please consult the supported codec list in the ffmpeg |
|
documentation. |
|
|
|
@section Which codecs are supported by Windows? |
|
|
|
Windows does not support standard formats like MPEG very well, unless you |
|
install some additional codecs. |
|
|
|
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 |
|
Only if you have some MPEG-4 codec like ffdshow or Xvid installed. |
|
@item mpeg1 |
|
.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 |
|
@item pcm |
|
always |
|
@item mp3 |
|
If some MP3 codec like LAME is installed. |
|
@end table |
|
|
|
|
|
@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. |
|
|
|
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... |
|
|
|
@chapter Usage |
|
|
|
@section ffmpeg does not work; what is wrong? |
|
|
|
Try a @code{make distclean} in the ffmpeg source directory before the build. If this does not help see |
|
(@url{http://libav.org/bugreports.html}). |
|
|
|
@section How do I encode single pictures into movies? |
|
|
|
First, rename your pictures to follow a numerical sequence. |
|
For example, img1.jpg, img2.jpg, img3.jpg,... |
|
Then you may run: |
|
|
|
@example |
|
ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg |
|
@end example |
|
|
|
Notice that @samp{%d} is replaced by the image number. |
|
|
|
@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc... |
|
|
|
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 |
|
x=1; for i in *jpg; do counter=$(printf %03d $x); ln -s "$i" /tmp/img"$counter".jpg; x=$(($x+1)); done |
|
@end example |
|
|
|
If you want to sequence them by oldest modified first, substitute |
|
@code{$(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 |
|
|
|
The same logic is used for any image format that ffmpeg reads. |
|
|
|
@section How do I encode movie to single pictures? |
|
|
|
Use: |
|
|
|
@example |
|
ffmpeg -i movie.mpg movie%d.jpg |
|
@end example |
|
|
|
The @file{movie.mpg} used as input will be converted to |
|
@file{movie1.jpg}, @file{movie2.jpg}, etc... |
|
|
|
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 |
|
ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg |
|
@end example |
|
|
|
Beware that there is no "jpeg" codec. Use "mjpeg" instead. |
|
|
|
@section Why do I see a slight quality degradation with multithreaded MPEG* encoding? |
|
|
|
For multithreaded MPEG* encoding, the encoded slices must be independent, |
|
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. |
|
|
|
@section How can I read from the standard input or write to the standard output? |
|
|
|
Use @file{-} as file name. |
|
|
|
@section -f jpeg doesn't work. |
|
|
|
Try '-f image2 test%d.jpg'. |
|
|
|
@section Why can I not change the framerate? |
|
|
|
Some codecs, like MPEG-1/2, only allow a small number of fixed framerates. |
|
Choose a different codec with the -vcodec command line option. |
|
|
|
@section How do I encode Xvid or DivX video with ffmpeg? |
|
|
|
Both Xvid and DivX (version 4+) are implementations of the ISO MPEG-4 |
|
standard (note that there are many other coding formats that use this |
|
same standard). Thus, use '-vcodec mpeg4' to encode in these formats. The |
|
default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want |
|
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 |
|
default. |
|
|
|
@section How do I encode videos which play on the iPod? |
|
|
|
@table @option |
|
@item needed stuff |
|
-acodec libfaac -vcodec mpeg4 width<=320 height<=240 |
|
@item working stuff |
|
mv4, title |
|
@item non-working stuff |
|
B-frames |
|
@item example command line |
|
ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -mbd 2 -flags +mv4 -trellis 2 -aic 2 -cmp 2 -subcmp 2 -s 320x180 -metadata title=X output.mp4 |
|
@end table |
|
|
|
@section How do I encode videos which play on the PSP? |
|
|
|
@table @option |
|
@item needed stuff |
|
-acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp |
|
@item working stuff |
|
mv4, title |
|
@item non-working stuff |
|
B-frames |
|
@item example command line |
|
ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -ar 24000 -mbd 2 -flags +mv4 -trellis 2 -aic 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -metadata title=X -f psp output.mp4 |
|
@item needed stuff for H.264 |
|
-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 |
|
@item working stuff for H.264 |
|
title, loop filter |
|
@item non-working stuff for H.264 |
|
CAVLC |
|
@item example command line |
|
ffmpeg -i input -acodec libfaac -ab 128kb -vcodec libx264 -b 1200kb -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 |
|
@item higher resolution for newer PSP firmwares, width<=480, height<=272 |
|
-vcodec libx264 -level 21 -coder 1 -f psp |
|
@item example command line |
|
ffmpeg -i input -acodec libfaac -ab 128kb -ac 2 -ar 48000 -vcodec libx264 -level 21 -b 640kb -coder 1 -f psp -flags +loop -trellis 2 -partitions +parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 -g 250 -s 480x272 output.mp4 |
|
@end table |
|
|
|
@section Which are good parameters for encoding high quality MPEG-4? |
|
|
|
'-mbd rd -flags +mv4+aic -trellis 2 -cmp 2 -subcmp 2 -g 300 -pass 1/2', |
|
things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'. |
|
|
|
@section Which are good parameters for encoding high quality MPEG-1/MPEG-2? |
|
|
|
'-mbd rd -trellis 2 -cmp 2 -subcmp 2 -g 100 -pass 1/2' |
|
but beware the '-g 100' might cause problems with some decoders. |
|
Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd. |
|
|
|
@section Interlaced video looks very bad when encoded with ffmpeg, what is wrong? |
|
|
|
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. |
|
|
|
@section How can I read DirectShow files? |
|
|
|
If you have built Libav with @code{./configure --enable-avisynth} |
|
(only possible on MinGW/Cygwin platforms), |
|
then you may use any file that DirectShow can read as input. |
|
|
|
Just create an "input.avs" text file with this single line ... |
|
@example |
|
DirectShowSource("C:\path to your file\yourfile.asf") |
|
@end example |
|
... and then feed that text file to FFmpeg: |
|
@example |
|
ffmpeg -i input.avs |
|
@end example |
|
|
|
For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}. |
|
|
|
@section How can I join video files? |
|
|
|
A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by |
|
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 |
|
equally humble @code{copy} under Windows), and finally transcoding back to your |
|
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. |
|
|
|
Also notice that you may avoid the huge intermediate files by taking advantage |
|
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 |\ |
|
ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi |
|
@end example |
|
|
|
Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also |
|
allow concatenation, and the transcoding step is almost lossless. |
|
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. |
|
|
|
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 & |
|
@{ ffmpeg -i input2.flv -an -f yuv4mpegpipe - < /dev/null | tail -n +2 > temp2.v ; @} & |
|
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 |
|
|
|
@section FFmpeg does not adhere to the -maxrate setting, some frames are bigger than maxrate/fps. |
|
|
|
Read the MPEG spec about video buffer verifier. |
|
|
|
@section I want CBR, but no matter what I do frame sizes differ. |
|
|
|
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 |
|
constant, the output can vary as needed. |
|
|
|
@section How do I check if a stream is CBR? |
|
|
|
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." |
|
|
|
|
|
@chapter Development |
|
|
|
@section Are there examples illustrating how to use the Libav libraries, particularly libavcodec and libavformat? |
|
|
|
Yes. Read the Developers Guide of the Libav documentation. Alternatively, |
|
examine the source code for one of the many open source projects that |
|
already incorporate Libav at (@url{projects.html}). |
|
|
|
@section Can you support my C compiler XXX? |
|
|
|
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. |
|
|
|
@section Is Microsoft Visual C++ supported? |
|
|
|
No. Microsoft Visual C++ is not compliant to the C99 standard and does |
|
not - among other things - support the inline assembly used in Libav. |
|
If you wish to use MSVC++ for your |
|
project then you can link the MSVC++ code with libav* as long as |
|
you compile the latter with a working C compiler. For more information, see |
|
the @emph{Microsoft Visual C++ compatibility} section in the Libav |
|
documentation. |
|
|
|
There have been efforts to make Libav compatible with MSVC++ in the |
|
past. However, they have all been rejected as too intrusive, especially |
|
since MinGW does the job adequately. None of the core developers |
|
work with MSVC++ and thus this item is low priority. Should you find |
|
the silver bullet that solves this problem, feel free to shoot it at us. |
|
|
|
We strongly recommend you to move over from MSVC++ to MinGW tools. |
|
|
|
@section Can I use Libav or libavcodec under Windows? |
|
|
|
Yes, but the Cygwin or MinGW tools @emph{must} be used to compile Libav. |
|
Read the @emph{Windows} section in the Libav documentation to find more |
|
information. |
|
|
|
@section Can you add automake, libtool or autoconf support? |
|
|
|
No. These tools are too bloated and they complicate the build. |
|
|
|
@section Why not rewrite ffmpeg in object-oriented C++? |
|
|
|
Libav is already organized in a highly modular manner and does not need to |
|
be rewritten in a formal object language. Further, many of the developers |
|
favor straight C; it works for them. For more arguments on this matter, |
|
read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}). |
|
|
|
@section Why are the ffmpeg programs devoid of debugging symbols? |
|
|
|
The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug |
|
information. Those binaries are stripped to create ffmpeg, ffplay, etc. If |
|
you need the debug information, use the *_g versions. |
|
|
|
@section I do not like the LGPL, can I contribute code under the GPL instead? |
|
|
|
Yes, as long as the code is optional and can easily and cleanly be placed |
|
under #if CONFIG_GPL without breaking anything. So for example a new codec |
|
or filter would be OK under GPL while a bug fix to LGPL code would not. |
|
|
|
@section I want to compile xyz.c alone but my compiler produced many errors. |
|
|
|
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. |
|
|
|
@section I'm using libavcodec from within my C++ application but the linker complains about missing symbols which seem to be available. |
|
|
|
Libav is a pure C project, so to use the libraries within your C++ application |
|
you need to explicitly state that you are using a C library. You can do this by |
|
encompassing your Libav includes using @code{extern "C"}. |
|
|
|
See @url{http://www.parashift.com/c++-faq-lite/mixing-c-and-cpp.html#faq-32.3} |
|
|
|
@section I have a file in memory / a API different from *open/*read/ libc how do I use it with libavformat? |
|
|
|
You have to implement a URLProtocol, see @file{libavformat/file.c} in |
|
Libav and @file{libmpdemux/demux_lavf.c} in MPlayer sources. |
|
|
|
@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. |
|
|
|
@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. |
|
|
|
@section Where can I find libav* headers for Pascal/Delphi? |
|
|
|
see @url{http://www.iversenit.dk/dev/ffmpeg-headers/} |
|
|
|
@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm? |
|
|
|
see @url{http://www.ffmpeg.org/~michael/} |
|
|
|
@section How do I feed H.263-RTP (and other codecs in RTP) to libavcodec? |
|
|
|
Even if peculiar since it is network oriented, RTP is a container like any |
|
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. |
|
|
|
@section AVStream.r_frame_rate is wrong, it is much larger than the framerate. |
|
|
|
r_frame_rate is NOT the average framerate, it is the smallest framerate |
|
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 |
|
will be 150. |
|
|
|
@bye
|
|
|