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1 7ff56c72 Fabrice Bellard
\input texinfo @c -*- texinfo -*-
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@settitle FFmpeg FAQ
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@titlepage
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@sp 7
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@center @titlefont{FFmpeg FAQ}
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@sp 3
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@end titlepage
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@chapter General Problems
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13 cacf7199 Mike Melanson
@section I cannot read this file although this format seems to be supported by ffmpeg.
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Even if ffmpeg can read the file format, it may not support all its
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codecs. Please consult the supported codec list in the ffmpeg
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documentation.
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@section How do I encode single pictures to movies?
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First, rename your pictures to follow a numerical sequence.
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For example, img1.jpg, img2.jpg, img3.jpg,...
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Then you may run:
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@example
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  ffmpeg -f image2 -i img%d.jpg /tmp/a.mpg
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@end example
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Notice that @samp{%d} is replaced by the image number.
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@file{img%03d.jpg} means the sequence @file{img001.jpg}, @file{img002.jpg}, etc...
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The same logic is used for any image format that ffmpeg reads.
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@section How do I encode movie to single pictures?
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37 3c88ea24 Baptiste Coudurier
Use:
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@example
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  ffmpeg -i movie.mpg movie%d.jpg
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@end example
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The @file{movie.mpg} used as input will be converted to
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@file{movie1.jpg}, @file{movie2.jpg}, etc...
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Instead of relying on file format self-recognition, you may also use
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@table @option
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@item -vcodec ppm
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@item -vcodec png
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@item -vcodec mjpeg
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@end table
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to force the encoding.
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Applying that to the previous example:
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@example
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  ffmpeg -i movie.mpg -f image2 -vcodec mjpeg menu%d.jpg
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@end example
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Beware that there is no "jpeg" codec. Use "mjpeg" instead.
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@section FFmpeg does not support codec XXX. Can you include a Windows DLL loader to support it?
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No. FFmpeg only supports open source codecs. Windows DLLs are not
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portable, bloated and often slow.
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@section I get "Unsupported codec (id=86043) for input stream #0.1". What is the problem?
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This is the Qcelp codec, FFmpeg has no support for that codec currently. Try mencoder/mplayer it might work.
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@section Why do I see a slight quality degradation with multithreaded MPEG* encoding?
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For multithreaded MPEG* encoding, the encoded slices must be independent,
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otherwise thread n would practically have to wait for n-1 to finish, so it's
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quite logical that there is a small reduction of quality. This is not a bug.
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@section How can I read from the standard input or write to the standard output?
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Use @file{-} as filename.
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@section Why does ffmpeg not decode audio in VOB files?
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The audio is AC3 (a.k.a. A/52). AC3 decoding is an optional component in ffmpeg
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as the component that handles AC3 decoding (liba52) is currently released under
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the GPL. If you have liba52 installed on your system, enable AC3 decoding
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with @code{./configure --enable-liba52 --enable-gpl}. Take care: by
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enabling AC3, you automatically change the license of libavcodec from
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LGPL to GPL.
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@section Which codecs are supported by Windows?
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Windows does not support standard formats like MPEG very well, unless you
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install some additional codecs
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The following list of video codecs should work on most Windows systems:
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@table @option
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@item msmpeg4v2
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.avi/.asf
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@item msmpeg4
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.asf only
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@item wmv1
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.asf only
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@item wmv2
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.asf only
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@item mpeg4
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only if you have some MPEG-4 codec installed like ffdshow or XviD
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@item mpeg1
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.mpg only
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@end table
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Note, ASF files often have .wmv or .wma extensions in Windows. It should also
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be mentioned that Microsoft claims a patent on the ASF format, and may sue
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or threaten users who create ASF files with non-Microsoft software. It is
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strongly advised to avoid ASF where possible.
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The following list of audio codecs should work on most Windows systems:
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@table @option
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@item adpcm_ima_wav
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@item adpcm_ms
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@item pcm
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@item mp3
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if some MP3 codec like LAME is installed
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@end table
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@section Why does the chrominance data seem to be sampled at a different time from the luminance data on bt8x8 captures on Linux?
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This is a well-known bug in the bt8x8 driver. For 2.4.26 there is a patch at
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(@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-420-2.4.26.patch?view=co}). This may also
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apply cleanly to other 2.4-series kernels.
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129 87759af9 Diego Biurrun
@section How do I avoid the ugly aliasing artifacts in bt8x8 captures on Linux?
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131 cacf7199 Mike Melanson
Pass 'combfilter=1 lumafilter=1' to the bttv driver. Note though that 'combfilter=1'
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will cause somewhat too strong filtering. A fix is to apply (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.4.26.patch?view=co})
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or (@url{http://svn.mplayerhq.hu/michael/trunk/patches/bttv-comb-2.6.6.patch?view=co})
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and pass 'combfilter=2'.
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136 9ba42958 Diego Biurrun
@section I have a problem with an old version of ffmpeg; where should I report it?
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Nowhere. Upgrade to the latest release or if there is no recent release upgrade
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to Subversion HEAD. You could also try to report it. Maybe you will get lucky and
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become the first person in history to get an answer different from "upgrade
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to Subversion HEAD".
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@section -f jpeg doesn't work.
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Try '-f image2 test%d.jpg'.
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@section Why can I not change the framerate?
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Some codecs, like MPEG-1/2, only allow a small number of fixed framerates.
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Choose a different codec with the -vcodec command line option.
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@section ffmpeg does not work; What is wrong?
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Try a 'make distclean' in the ffmpeg source directory before the build. If this does not help see
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(@url{http://ffmpeg.org/bugreports.php}).
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@section How do I encode XviD or DivX video with ffmpeg?
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Both XviD and DivX (version 4+) are implementations of the ISO MPEG-4
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standard (note that there are many other coding formats that use this
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same standard). Thus, use '-vcodec mpeg4' to encode these formats. The
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default fourcc stored in an MPEG-4-coded file will be 'FMP4'. If you want
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a different fourcc, use the '-vtag' option. E.g., '-vtag xvid' will
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force the fourcc 'xvid' to be stored as the video fourcc rather than the
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default.
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@section How do I encode videos which play on the iPod?
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@table @option
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@item needed stuff
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-acodec libfaac -vcodec mpeg4 width<=320 height<=240
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@item working stuff
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4mv, title
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@item non-working stuff
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B-frames
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@item example command line
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ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 320x180 -title X output.mp4
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@end table
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@section How do I encode videos which play on the PSP?
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@table @option
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@item needed stuff
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-acodec libfaac -vcodec mpeg4 width*height<=76800 width%16=0 height%16=0 -ar 24000 -r 30000/1001 or 15000/1001 -f psp
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@item working stuff
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4mv, title
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@item non-working stuff
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B-frames
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@item example command line
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ffmpeg -i input -acodec libfaac -ab 128kb -vcodec mpeg4 -b 1200kb -ar 24000 -mbd 2 -flags +4mv+trell -aic 2 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp output.mp4
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@item needed stuff for H.264
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-acodec libfaac -vcodec h264 width*height<=76800 width%16=0? height%16=0? -ar 48000 -coder 1 -r 30000/1001 or 15000/1001 -f psp
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@item working stuff for H.264
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title, loop filter
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@item non-working stuff for H.264
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CAVLC
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@item example command line
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ffmpeg -i input -acodec libfaac -ab 128kb -vcodec h264 -b 1200kb -ar 48000 -mbd 2 -coder 1 -cmp 2 -subcmp 2 -s 368x192 -r 30000/1001 -title X -f psp -flags loop -trellis 2 -partitions parti4x4+parti8x8+partp4x4+partp8x8+partb8x8 output.mp4
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@end table
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@section Which are good parameters for encoding high quality MPEG-4?
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'-mbd rd -flags +4mv+trell+aic -cmp 2 -subcmp 2 -g 300 -pass 1/2',
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things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd'.
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@section Which are good parameters for encoding high quality MPEG-1/MPEG-2?
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'-mbd rd -flags +trell -cmp 2 -subcmp 2 -g 100 -pass 1/2'
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but beware the '-g 100' might cause problems with some decoders.
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Things to try: '-bf 2', '-flags qprd', '-flags mv0', '-flags skiprd.
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@section Interlaced video looks very bad when encoded with ffmpeg, whats wrong?
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You should use '-flags +ilme+ildct' and maybe '-flags +alt' for interlaced
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material, and try '-top 0/1' if the result looks really messed-up.
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@section How can I read DirectShow files?
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If you have built FFmpeg with @code{./configure --enable-avisynth}
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(only possible on MinGW/Cygwin platforms),
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then you may use any file that DirectShow can read as input.
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(Be aware that this feature has been recently added,
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so you will need to help yourself in case of problems.)
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Just create an "input.avs" text file with this single line ...
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@example
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  DirectShowSource("C:\path to your file\yourfile.asf")
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@end example
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... and then feed that text file to FFmpeg:
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@example
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  ffmpeg -i input.avs
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@end example
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For ANY other help on Avisynth, please visit @url{http://www.avisynth.org/}.
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@section My bugreport/mail to ffmpeg-devel/user has not received any replies.
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Likely reasons
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@itemize
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@item We are busy and haven't had time yet to read your report or
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investigate the issue.
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@item You didn't follow bugreports.html.
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@item You didn't use Subversion HEAD.
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@item You reported a segmentation fault without gdb output.
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@item You describe a problem but not how to reproduce it.
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@item It's unclear if you use ffmpeg as command line tool or use
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libav* from another application.
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@item You speak about a video having problems on playback but
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not what you use to play it.
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@item We have no faint clue what you are talking about besides
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that it is related to FFmpeg.
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@end itemize
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@section How can I join video files?
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A few multimedia containers (MPEG-1, MPEG-2 PS, DV) allow to join video files by
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merely concatenating them.
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Hence you may concatenate your multimedia files by first transcoding them to
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these privileged formats, then using the humble @code{cat} command (or the
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equally humble @code{copy} under Windows), and finally transcoding back to your
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format of choice.
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@example
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ffmpeg -i input1.avi -sameq intermediate1.mpg
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ffmpeg -i input2.avi -sameq intermediate2.mpg
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cat intermediate1.mpg intermediate2.mpg > intermediate_all.mpg
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ffmpeg -i intermediate_all.mpg -sameq output.avi
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@end example
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Notice that you should either use @code{-sameq} or set a reasonably high
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bitrate for your intermediate and output files, if you want to preserve
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video quality.
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Also notice that you may avoid the huge intermediate files by taking advantage
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of named pipes, should your platform support it:
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@example
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mkfifo intermediate1.mpg
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mkfifo intermediate2.mpg
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ffmpeg -i input1.avi -sameq -y intermediate1.mpg < /dev/null &
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ffmpeg -i input2.avi -sameq -y intermediate2.mpg < /dev/null &
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cat intermediate1.mpg intermediate2.mpg |\
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ffmpeg -f mpeg -i - -sameq -vcodec mpeg4 -acodec libmp3lame output.avi
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@end example
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Similarly, the yuv4mpegpipe format, and the raw video, raw audio codecs also
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allow concatenation, and the transcoding step is almost lossless.
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For example, let's say we want to join two FLV files into an output.flv file:
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@example
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mkfifo temp1.a
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mkfifo temp1.v
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mkfifo temp2.a
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mkfifo temp2.v
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mkfifo all.a
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mkfifo all.v
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ffmpeg -i input1.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp1.a < /dev/null &
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ffmpeg -i input2.flv -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 - > temp2.a < /dev/null &
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ffmpeg -i input1.flv -an -f yuv4mpegpipe - > temp1.v < /dev/null &
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ffmpeg -i input2.flv -an -f yuv4mpegpipe - > temp2.v < /dev/null &
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cat temp1.a temp2.a > all.a &
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cat temp1.v temp2.v > all.v &
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ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i all.a \
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       -f yuv4mpegpipe -i all.v \
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       -sameq -y output.flv
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rm temp[12].[av] all.[av]
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@end example
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@chapter Development
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@section When will the next FFmpeg version be released? / Why are FFmpeg releases so few and far between?
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Like most open source projects FFmpeg suffers from a certain lack of
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manpower. For this reason the developers have to prioritize the work
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they do and putting out releases is not at the top of the list, fixing
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bugs and reviewing patches takes precedence. Please don't complain or
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request more timely and/or frequent releases unless you are willing to
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help out creating them.
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@section Why doesn't FFmpeg support feature [xyz]?
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Because no one has taken on that task yet. FFmpeg development is
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driven by the tasks that are important to the individual developers.
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If there is a feature that is important to you, the best way to get
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it implemented is to undertake the task yourself.
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@section Are there examples illustrating how to use the FFmpeg libraries, particularly libavcodec and libavformat?
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Yes. Read the Developers Guide of the FFmpeg documentation. Alternatively,
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examine the source code for one of the many open source projects that
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already incorporate ffmpeg at (@url{projects.php}).
334 a93b9dba Fabrice Bellard
335 5965e1a9 Víctor Paesa
@section Can you support my C compiler XXX?
336 7ff56c72 Fabrice Bellard
337 e867d9b9 Diego Biurrun
It depends. If your compiler is C99-compliant, then patches to support
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it are likely to be welcome if they do not pollute the source code
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with @code{#ifdef}s related to the compiler.
340 7ff56c72 Fabrice Bellard
341 2f0b8fbb Diego Biurrun
@section Visual C++ produces many errors.
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Visual C++ is not compliant to the C standard and does not support
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the inline assembly used in FFmpeg.
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If you wish - for whatever weird reason - to use Visual C++ for your
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project then you can link the Visual C++ code with libav* as long as
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you compile the latter with a working C compiler. For more information, see
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the @emph{Visual C++ compatibility} section in the FFmpeg documentation.
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There have been efforts to make FFmpeg compatible with Visual C++ in the
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past. However, they have all been rejected as too intrusive, especially
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since MinGW does the job perfectly adequately. None of the core developers
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work with Visual C++ and thus this item is low priority. Should you find
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the silver bullet that solves this problem, feel free to shoot it at us.
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@section Can I use FFmpeg or libavcodec under Windows?
357 7ff56c72 Fabrice Bellard
358 988a9f9e Fabrice Bellard
Yes, but the MinGW tools @emph{must} be used to compile FFmpeg. You
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can link the resulting DLLs with any other Windows program. Read the
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@emph{Native Windows Compilation} and @emph{Visual C++ compatibility}
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sections in the FFmpeg documentation to find more information.
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To get help and instructions for using FFmpeg under Windows, check out
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the FFmpeg Windows Help Forum at
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@url{http://arrozcru.no-ip.org/ffmpeg/}.
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@section Can you add automake, libtool or autoconf support?
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No. These tools are too bloated and they complicate the build.
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371 5965e1a9 Víctor Paesa
@section Why not rewrite ffmpeg in object-oriented C++?
372 fbf33e4f Michael Niedermayer
373 87759af9 Diego Biurrun
ffmpeg is already organized in a highly modular manner and does not need to
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be rewritten in a formal object language. Further, many of the developers
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favor straight C; it works for them. For more arguments on this matter,
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read "Programming Religion" at (@url{http://www.tux.org/lkml/#s15}).
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378 5965e1a9 Víctor Paesa
@section Why are the ffmpeg programs devoid of debugging symbols?
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The build process creates ffmpeg_g, ffplay_g, etc. which contain full debug
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information. Those binaries are strip'd to create ffmpeg, ffplay, etc. If
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you need the debug information, used the *_g versions.
383 fbf33e4f Michael Niedermayer
384 5965e1a9 Víctor Paesa
@section I do not like the LGPL, can I contribute code under the GPL instead?
385 61a1e081 Michael Niedermayer
386 e180129f Diego Biurrun
Yes, as long as the code is optional and can easily and cleanly be placed
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under #ifdef CONFIG_GPL without breaking anything. So for example a new codec
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or filter would be OK under GPL while a bugfix to LGPL code would not.
389 61a1e081 Michael Niedermayer
390 e180129f Diego Biurrun
@section I want to compile xyz.c alone but my compiler produced many errors.
391 61a1e081 Michael Niedermayer
392 e180129f Diego Biurrun
Common code is in its own files in libav* and is used by the individual
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codecs. They will not work without the common parts, you have to compile
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the whole libav*. If you wish, disable some parts with configure switches.
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You can also try to hack it and remove more, but if you had problems fixing
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the compilation failure then you are probably not qualified for this.
397 61a1e081 Michael Niedermayer
398 5965e1a9 Víctor Paesa
@section I have a file in memory / a API different from *open/*read/ libc how do i use it with libavformat?
399 f994f61e Michael Niedermayer
400 1c1b5a40 Diego Biurrun
You have to implement a URLProtocol, see libavformat/file.c in FFmpeg
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and libmpdemux/demux_lavf.c in MPlayer sources.
402 f994f61e Michael Niedermayer
403 e9766450 Ramiro Polla
@section I get "No compatible shell script interpreter found." in MSys.
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The standard MSys bash (2.04) is broken. You need to install 2.05 or later.
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407 5c159f40 Diego Biurrun
@section I tried to pass RTP packets into a decoder, but it doesn't work.
408 b72ad042 Michael Niedermayer
409 241fb0c4 Luca Barbato
RTP is a container format like any other, you must first depacketize the
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codec frames/samples stored in RTP and then feed to the decoder.
411 b72ad042 Michael Niedermayer
412 7c1ebf17 Diego Biurrun
@section Where can I find libav* headers for Pascal/Delphi?
413 04704a78 Michael Niedermayer
414
see @url{http://www.iversenit.dk/dev/ffmpeg-headers/}
415
416 7c1ebf17 Diego Biurrun
@section Where is the documentation about ffv1, msmpeg4, asv1, 4xm?
417 afe28f7c Michael Niedermayer
418
see @url{http://svn.mplayerhq.hu/michael/trunk/docs/}
419
420 33ed2d84 Luca Barbato
@section how do I feed H.263-RTP (and other codecs in RTP) to libavcodec?
421 8749180c Michael Niedermayer
422 241fb0c4 Luca Barbato
Even if peculiar since it is network oriented, RTP is a container like any
423 33ed2d84 Luca Barbato
other. You have to @emph{demux} RTP before feeding the payload to libavcodec.
424
In this specific case please look at RFC 4629 to see how it should be done.
425 8749180c Michael Niedermayer
426 7ff56c72 Fabrice Bellard
@bye