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\input texinfo @c -*- texinfo -*-
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@settitle FFmpeg Documentation
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@titlepage
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@sp 7
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@center @titlefont{FFmpeg Documentation}
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@sp 3
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@end titlepage
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@chapter Introduction
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FFmpeg is a very fast video and audio converter. It can also grab from
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a live audio/video source.
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The command line interface is designed to be intuitive, in the sense
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that FFmpeg tries to figure out all parameters that can possibly be
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derived automatically. You usually only have to specify the target
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bitrate you want.
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FFmpeg can also convert from any sample rate to any other, and resize
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video on the fly with a high quality polyphase filter.
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@chapter Quick Start
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@c man begin EXAMPLES
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@section Video and Audio grabbing
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FFmpeg can grab video and audio from devices given that you specify the input
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format and device.
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@example
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ffmpeg -f oss -i /dev/dsp -f video4linux2 -i /dev/video0 /tmp/out.mpg
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@end example
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Note that you must activate the right video source and channel before
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launching FFmpeg with any TV viewer such as xawtv
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(@url{http://linux.bytesex.org/xawtv/}) by Gerd Knorr. You also
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have to set the audio recording levels correctly with a
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standard mixer.
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@section X11 grabbing
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FFmpeg can grab the X11 display.
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@example
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ffmpeg -f x11grab -s cif -i :0.0 /tmp/out.mpg
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@end example
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0.0 is display.screen number of your X11 server, same as
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the DISPLAY environment variable.
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@example
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ffmpeg -f x11grab -s cif -i :0.0+10,20 /tmp/out.mpg
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@end example
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0.0 is display.screen number of your X11 server, same as the DISPLAY environment
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variable. 10 is the x-offset and 20 the y-offset for the grabbing.
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@section Video and Audio file format conversion
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* FFmpeg can use any supported file format and protocol as input:
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Examples:
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* You can use YUV files as input:
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@example
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ffmpeg -i /tmp/test%d.Y /tmp/out.mpg
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@end example
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It will use the files:
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@example
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/tmp/test0.Y, /tmp/test0.U, /tmp/test0.V,
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/tmp/test1.Y, /tmp/test1.U, /tmp/test1.V, etc...
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@end example
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The Y files use twice the resolution of the U and V files. They are
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raw files, without header. They can be generated by all decent video
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decoders. You must specify the size of the image with the @option{-s} option
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if FFmpeg cannot guess it.
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* You can input from a raw YUV420P file:
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@example
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ffmpeg -i /tmp/test.yuv /tmp/out.avi
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@end example
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test.yuv is a file containing raw YUV planar data. Each frame is composed
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of the Y plane followed by the U and V planes at half vertical and
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horizontal resolution.
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* You can output to a raw YUV420P file:
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@example
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ffmpeg -i mydivx.avi hugefile.yuv
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@end example
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* You can set several input files and output files:
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@example
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ffmpeg -i /tmp/a.wav -s 640x480 -i /tmp/a.yuv /tmp/a.mpg
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@end example
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Converts the audio file a.wav and the raw YUV video file a.yuv
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to MPEG file a.mpg.
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* You can also do audio and video conversions at the same time:
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@example
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ffmpeg -i /tmp/a.wav -ar 22050 /tmp/a.mp2
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@end example
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Converts a.wav to MPEG audio at 22050 Hz sample rate.
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* You can encode to several formats at the same time and define a
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mapping from input stream to output streams:
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@example
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ffmpeg -i /tmp/a.wav -ab 64k /tmp/a.mp2 -ab 128k /tmp/b.mp2 -map 0:0 -map 0:0
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@end example
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Converts a.wav to a.mp2 at 64 kbits and to b.mp2 at 128 kbits. '-map
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file:index' specifies which input stream is used for each output
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stream, in the order of the definition of output streams.
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* You can transcode decrypted VOBs:
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@example
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ffmpeg -i snatch_1.vob -f avi -vcodec mpeg4 -b 800k -g 300 -bf 2 -acodec libmp3lame -ab 128k snatch.avi
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@end example
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This is a typical DVD ripping example; the input is a VOB file, the
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output an AVI file with MPEG-4 video and MP3 audio. Note that in this
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command we use B-frames so the MPEG-4 stream is DivX5 compatible, and
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GOP size is 300 which means one intra frame every 10 seconds for 29.97fps
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input video. Furthermore, the audio stream is MP3-encoded so you need
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to enable LAME support by passing @code{--enable-libmp3lame} to configure.
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The mapping is particularly useful for DVD transcoding
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to get the desired audio language.
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NOTE: To see the supported input formats, use @code{ffmpeg -formats}.
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* You can extract images from a video, or create a video from many images:
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For extracting images from a video:
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@example
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ffmpeg -i foo.avi -r 1 -s WxH -f image2 foo-%03d.jpeg
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@end example
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This will extract one video frame per second from the video and will
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output them in files named @file{foo-001.jpeg}, @file{foo-002.jpeg},
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etc. Images will be rescaled to fit the new WxH values.
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If you want to extract just a limited number of frames, you can use the
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above command in combination with the -vframes or -t option, or in
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combination with -ss to start extracting from a certain point in time.
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For creating a video from many images:
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@example
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ffmpeg -f image2 -i foo-%03d.jpeg -r 12 -s WxH foo.avi
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@end example
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The syntax @code{foo-%03d.jpeg} specifies to use a decimal number
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composed of three digits padded with zeroes to express the sequence
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number. It is the same syntax supported by the C printf function, but
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only formats accepting a normal integer are suitable.
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* You can put many streams of the same type in the output:
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@example
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ffmpeg -i test1.avi -i test2.avi -vcodec copy -acodec copy -vcodec copy -acodec copy test12.avi -newvideo -newaudio
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@end example
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In addition to the first video and audio streams, the resulting
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output file @file{test12.avi} will contain the second video
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and the second audio stream found in the input streams list.
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The @code{-newvideo}, @code{-newaudio} and @code{-newsubtitle}
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options have to be specified immediately after the name of the output
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file to which you want to add them.
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@c man end
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@chapter Invocation
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@section Syntax
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The generic syntax is:
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@example
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@c man begin SYNOPSIS
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ffmpeg [[infile options][@option{-i} @var{infile}]]... @{[outfile options] @var{outfile}@}...
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@c man end
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@end example
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@c man begin DESCRIPTION
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As a general rule, options are applied to the next specified
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file. Therefore, order is important, and you can have the same
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option on the command line multiple times. Each occurrence is
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then applied to the next input or output file.
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* To set the video bitrate of the output file to 64kbit/s:
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@example
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ffmpeg -i input.avi -b 64k output.avi
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@end example
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* To force the frame rate of the output file to 24 fps:
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@example
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ffmpeg -i input.avi -r 24 output.avi
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@end example
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* To force the frame rate of the input file (valid for raw formats only)
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to 1 fps and the frame rate of the output file to 24 fps:
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@example
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ffmpeg -r 1 -i input.m2v -r 24 output.avi
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@end example
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The format option may be needed for raw input files.
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By default, FFmpeg tries to convert as losslessly as possible: It
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uses the same audio and video parameters for the outputs as the one
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specified for the inputs.
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@c man end
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@c man begin OPTIONS
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@section Main options
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@table @option
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@item -L
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Show license.
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@item -h
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Show help.
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@item -version
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Show version.
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@item -formats
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Show available formats, codecs, bitstream filters, protocols, and frame size and frame rate abbreviations.
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The fields preceding the format and codec names have the following meanings:
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@table @samp
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@item D
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Decoding available
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@item E
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Encoding available
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@item V/A/S
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Video/audio/subtitle codec
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@item S
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Codec supports slices
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@item D
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Codec supports direct rendering
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@item T
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Codec can handle input truncated at random locations instead of only at frame boundaries
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@end table
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@item -f @var{fmt}
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Force format.
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@item -i @var{filename}
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input file name
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@item -y
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Overwrite output files.
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@item -t @var{duration}
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Restrict the transcoded/captured video sequence
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to the duration specified in seconds.
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@code{hh:mm:ss[.xxx]} syntax is also supported.
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@item -fs @var{limit_size}
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Set the file size limit.
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@item -ss @var{position}
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Seek to given time position in seconds.
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@code{hh:mm:ss[.xxx]} syntax is also supported.
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@item -itsoffset @var{offset}
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Set the input time offset in seconds.
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@code{[-]hh:mm:ss[.xxx]} syntax is also supported.
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This option affects all the input files that follow it.
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The offset is added to the timestamps of the input files.
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Specifying a positive offset means that the corresponding
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streams are delayed by 'offset' seconds.
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@item -title @var{string}
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Set the title.
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@item -timestamp @var{time}
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Set the timestamp.
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@item -author @var{string}
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Set the author.
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@item -copyright @var{string}
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Set the copyright.
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@item -comment @var{string}
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Set the comment.
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@item -album @var{string}
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Set the album.
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@item -track @var{number}
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Set the track.
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@item -year @var{number}
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Set the year.
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@item -v @var{number}
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Set the logging verbosity level.
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@item -target @var{type}
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Specify target file type ("vcd", "svcd", "dvd", "dv", "dv50", "pal-vcd",
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"ntsc-svcd", ... ). All the format options (bitrate, codecs,
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buffer sizes) are then set automatically. You can just type:
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@example
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ffmpeg -i myfile.avi -target vcd /tmp/vcd.mpg
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@end example
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Nevertheless you can specify additional options as long as you know
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they do not conflict with the standard, as in:
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@example
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ffmpeg -i myfile.avi -target vcd -bf 2 /tmp/vcd.mpg
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@end example
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@item -dframes @var{number}
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Set the number of data frames to record.
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@item -scodec @var{codec}
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Force subtitle codec ('copy' to copy stream).
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@item -newsubtitle
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Add a new subtitle stream to the current output stream.
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@item -slang @var{code}
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Set the ISO 639 language code (3 letters) of the current subtitle stream.
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@end table
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@section Video Options
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@table @option
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@item -b @var{bitrate}
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Set the video bitrate in bit/s (default = 200 kb/s).
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@item -vframes @var{number}
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Set the number of video frames to record.
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@item -r @var{fps}
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Set frame rate (Hz value, fraction or abbreviation), (default = 25).
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@item -s @var{size}
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Set frame size. The format is @samp{wxh} (ffserver default = 160x128, ffmpeg default = same as source).
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The following abbreviations are recognized:
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@table @samp
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@item sqcif
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128x96
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@item qcif
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176x144
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@item cif
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352x288
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@item 4cif
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704x576
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@item qqvga
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160x120
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@item qvga
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320x240
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@item vga
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640x480
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@item svga
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800x600
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@item xga
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1024x768
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@item uxga
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1600x1200
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@item qxga
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2048x1536
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@item sxga
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1280x1024
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@item qsxga
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2560x2048
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@item hsxga
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5120x4096
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@item wvga
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852x480
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@item wxga
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1366x768
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@item wsxga
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1600x1024
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@item wuxga
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1920x1200
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@item woxga
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2560x1600
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@item wqsxga
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3200x2048
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@item wquxga
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3840x2400
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@item whsxga
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6400x4096
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@item whuxga
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7680x4800
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@item cga
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320x200
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@item ega
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640x350
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@item hd480
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852x480
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@item hd720
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1280x720
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@item hd1080
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1920x1080
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@end table
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@item -aspect @var{aspect}
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Set aspect ratio (4:3, 16:9 or 1.3333, 1.7777).
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@item -croptop @var{size}
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Set top crop band size (in pixels).
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@item -cropbottom @var{size}
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Set bottom crop band size (in pixels).
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@item -cropleft @var{size}
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Set left crop band size (in pixels).
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@item -cropright @var{size}
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Set right crop band size (in pixels).
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@item -padtop @var{size}
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Set top pad band size (in pixels).
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@item -padbottom @var{size}
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Set bottom pad band size (in pixels).
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@item -padleft @var{size}
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Set left pad band size (in pixels).
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@item -padright @var{size}
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Set right pad band size (in pixels).
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@item -padcolor @var{hex_color}
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Set color of padded bands. The value for padcolor is expressed
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as a six digit hexadecimal number where the first two digits
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represent red, the middle two digits green and last two digits
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blue (default = 000000 (black)).
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@item -vn
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Disable video recording.
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@item -bt @var{tolerance}
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Set video bitrate tolerance (in bits, default 4000k).
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Has a minimum value of: (target_bitrate/target_framerate).
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In 1-pass mode, bitrate tolerance specifies how far ratecontrol is
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willing to deviate from the target average bitrate value. This is
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not related to min/max bitrate. Lowering tolerance too much has
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an adverse effect on quality.
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@item -maxrate @var{bitrate}
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Set max video bitrate (in bit/s).
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Requires -bufsize to be set.
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@item -minrate @var{bitrate}
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Set min video bitrate (in bit/s).
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Most useful in setting up a CBR encode:
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@example
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ffmpeg -i myfile.avi -b 4000k -minrate 4000k -maxrate 4000k -bufsize 1835k out.m2v
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@end example
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It is of little use elsewise.
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@item -bufsize @var{size}
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Set video buffer verifier buffer size (in bits).
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@item -vcodec @var{codec}
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Force video codec to @var{codec}. Use the @code{copy} special value to
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tell that the raw codec data must be copied as is.
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@item -sameq
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Use same video quality as source (implies VBR).
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@item -pass @var{n}
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Select the pass number (1 or 2). It is used to do two-pass
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video encoding. The statistics of the video are recorded in the first
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pass into a log file (see also the option -passlogfile),
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and in the second pass that log file is used to generate the video
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at the exact requested bitrate.
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On pass 1, you may just deactivate audio and set output to null,
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examples for Windows and Unix:
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@example
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ffmpeg -i foo.mov -vcodec libxvid -pass 1 -an -f rawvideo -y NUL
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ffmpeg -i foo.mov -vcodec libxvid -pass 1 -an -f rawvideo -y /dev/null
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@end example
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@item -passlogfile @var{prefix}
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Set two-pass log file name prefix to @var{prefix}, the default file name
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prefix is ``ffmpeg2pass''. The complete file name will be
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@file{PREFIX-N.log}, where N is a number specific to the output
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stream.
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@item -newvideo
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Add a new video stream to the current output stream.
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@end table
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@section Advanced Video Options
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@table @option
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@item -pix_fmt @var{format}
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Set pixel format. Use 'list' as parameter to show all the supported
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pixel formats.
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@item -sws_flags @var{flags}
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Set SwScaler flags (only available when compiled with swscale support).
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@item -g @var{gop_size}
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Set the group of pictures size.
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@item -intra
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Use only intra frames.
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@item -vdt @var{n}
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Discard threshold.
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@item -qscale @var{q}
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Use fixed video quantizer scale (VBR).
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@item -qmin @var{q}
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minimum video quantizer scale (VBR)
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@item -qmax @var{q}
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maximum video quantizer scale (VBR)
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@item -qdiff @var{q}
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maximum difference between the quantizer scales (VBR)
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@item -qblur @var{blur}
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video quantizer scale blur (VBR) (range 0.0 - 1.0)
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@item -qcomp @var{compression}
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video quantizer scale compression (VBR) (default 0.5).
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Constant of ratecontrol equation. Recommended range for default rc_eq: 0.0-1.0
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@item -lmin @var{lambda}
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minimum video lagrange factor (VBR)
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@item -lmax @var{lambda}
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max video lagrange factor (VBR)
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@item -mblmin @var{lambda}
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minimum macroblock quantizer scale (VBR)
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@item -mblmax @var{lambda}
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maximum macroblock quantizer scale (VBR)
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These four options (lmin, lmax, mblmin, mblmax) use 'lambda' units,
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but you may use the QP2LAMBDA constant to easily convert from 'q' units:
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@example
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ffmpeg -i src.ext -lmax 21*QP2LAMBDA dst.ext
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@end example
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@item -rc_init_cplx @var{complexity}
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initial complexity for single pass encoding
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@item -b_qfactor @var{factor}
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qp factor between P- and B-frames
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@item -i_qfactor @var{factor}
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qp factor between P- and I-frames
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@item -b_qoffset @var{offset}
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qp offset between P- and B-frames
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@item -i_qoffset @var{offset}
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qp offset between P- and I-frames
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@item -rc_eq @var{equation}
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Set rate control equation (@pxref{FFmpeg formula
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evaluator}) (default = @code{tex^qComp}).
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@item -rc_override @var{override}
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rate control override for specific intervals
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@item -me_method @var{method}
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Set motion estimation method to @var{method}.
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Available methods are (from lowest to best quality):
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@table @samp
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@item zero
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Try just the (0, 0) vector.
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@item phods
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@item log
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@item x1
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@item hex
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@item umh
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@item epzs
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(default method)
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@item full
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exhaustive search (slow and marginally better than epzs)
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@end table
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@item -dct_algo @var{algo}
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Set DCT algorithm to @var{algo}. Available values are:
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@table @samp
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@item 0
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FF_DCT_AUTO (default)
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@item 1
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FF_DCT_FASTINT
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@item 2
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FF_DCT_INT
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@item 3
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FF_DCT_MMX
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@item 4
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FF_DCT_MLIB
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@item 5
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FF_DCT_ALTIVEC
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@end table
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@item -idct_algo @var{algo}
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Set IDCT algorithm to @var{algo}. Available values are:
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@table @samp
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@item 0
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FF_IDCT_AUTO (default)
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@item 1
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FF_IDCT_INT
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@item 2
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FF_IDCT_SIMPLE
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@item 3
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FF_IDCT_SIMPLEMMX
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@item 4
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FF_IDCT_LIBMPEG2MMX
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@item 5
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FF_IDCT_PS2
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@item 6
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FF_IDCT_MLIB
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@item 7
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FF_IDCT_ARM
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@item 8
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FF_IDCT_ALTIVEC
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@item 9
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FF_IDCT_SH4
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@item 10
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FF_IDCT_SIMPLEARM
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@end table
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@item -er @var{n}
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Set error resilience to @var{n}.
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@table @samp
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@item 1
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FF_ER_CAREFUL (default)
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@item 2
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FF_ER_COMPLIANT
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@item 3
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FF_ER_AGGRESSIVE
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@item 4
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FF_ER_VERY_AGGRESSIVE
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@end table
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@item -ec @var{bit_mask}
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Set error concealment to @var{bit_mask}. @var{bit_mask} is a bit mask of
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the following values:
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@table @samp
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@item 1
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FF_EC_GUESS_MVS (default = enabled)
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@item 2
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FF_EC_DEBLOCK (default = enabled)
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@end table
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@item -bf @var{frames}
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Use 'frames' B-frames (supported for MPEG-1, MPEG-2 and MPEG-4).
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@item -mbd @var{mode}
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macroblock decision
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@table @samp
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@item 0
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FF_MB_DECISION_SIMPLE: Use mb_cmp (cannot change it yet in FFmpeg).
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@item 1
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FF_MB_DECISION_BITS: Choose the one which needs the fewest bits.
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@item 2
639
FF_MB_DECISION_RD: rate distortion
640
@end table
641

    
642
@item -4mv
643
Use four motion vector by macroblock (MPEG-4 only).
644
@item -part
645
Use data partitioning (MPEG-4 only).
646
@item -bug @var{param}
647
Work around encoder bugs that are not auto-detected.
648
@item -strict @var{strictness}
649
How strictly to follow the standards.
650
@item -aic
651
Enable Advanced intra coding (h263+).
652
@item -umv
653
Enable Unlimited Motion Vector (h263+)
654

    
655
@item -deinterlace
656
Deinterlace pictures.
657
@item -ilme
658
Force interlacing support in encoder (MPEG-2 and MPEG-4 only).
659
Use this option if your input file is interlaced and you want
660
to keep the interlaced format for minimum losses.
661
The alternative is to deinterlace the input stream with
662
@option{-deinterlace}, but deinterlacing introduces losses.
663
@item -psnr
664
Calculate PSNR of compressed frames.
665
@item -vstats
666
Dump video coding statistics to @file{vstats_HHMMSS.log}.
667
@item -vstats_file @var{file}
668
Dump video coding statistics to @var{file}.
669
@item -top @var{n}
670
top=1/bottom=0/auto=-1 field first
671
@item -dc @var{precision}
672
Intra_dc_precision.
673
@item -vtag @var{fourcc/tag}
674
Force video tag/fourcc.
675
@item -qphist
676
Show QP histogram.
677
@item -vbsf @var{bitstream_filter}
678
Bitstream filters available are "dump_extra", "remove_extra", "noise", "h264_mp4toannexb", "imxdump", "mjpegadump".
679
@example
680
ffmpeg -i h264.mp4 -vcodec copy -vbsf h264_mp4toannexb -an out.h264
681
@end example
682
@end table
683

    
684
@section Audio Options
685

    
686
@table @option
687
@item -aframes @var{number}
688
Set the number of audio frames to record.
689
@item -ar @var{freq}
690
Set the audio sampling frequency (default = 44100 Hz).
691
@item -ab @var{bitrate}
692
Set the audio bitrate in bit/s (default = 64k).
693
@item -ac @var{channels}
694
Set the number of audio channels (default = 1).
695
@item -an
696
Disable audio recording.
697
@item -acodec @var{codec}
698
Force audio codec to @var{codec}. Use the @code{copy} special value to
699
specify that the raw codec data must be copied as is.
700
@item -newaudio
701
Add a new audio track to the output file. If you want to specify parameters,
702
do so before @code{-newaudio} (@code{-acodec}, @code{-ab}, etc..).
703

    
704
Mapping will be done automatically, if the number of output streams is equal to
705
the number of input streams, else it will pick the first one that matches. You
706
can override the mapping using @code{-map} as usual.
707

    
708
Example:
709
@example
710
ffmpeg -i file.mpg -vcodec copy -acodec ac3 -ab 384k test.mpg -acodec mp2 -ab 192k -newaudio
711
@end example
712
@item -alang @var{code}
713
Set the ISO 639 language code (3 letters) of the current audio stream.
714
@end table
715

    
716
@section Advanced Audio options:
717

    
718
@table @option
719
@item -atag @var{fourcc/tag}
720
Force audio tag/fourcc.
721
@item -absf @var{bitstream_filter}
722
Bitstream filters available are "dump_extra", "remove_extra", "noise", "mp3comp", "mp3decomp".
723
@end table
724

    
725
@section Subtitle options:
726

    
727
@table @option
728
@item -scodec @var{codec}
729
Force subtitle codec ('copy' to copy stream).
730
@item -newsubtitle
731
Add a new subtitle stream to the current output stream.
732
@item -slang @var{code}
733
Set the ISO 639 language code (3 letters) of the current subtitle stream.
734
@item -sbsf @var{bitstream_filter}
735
Bitstream filters available are "mov2textsub", "text2movsub".
736
@example
737
ffmpeg -i file.mov -an -vn -sbsf mov2textsub -scodec copy -f rawvideo sub.txt
738
@end example
739
@end table
740

    
741
@section Audio/Video grab options
742

    
743
@table @option
744
@item -vc @var{channel}
745
Set video grab channel (DV1394 only).
746
@item -tvstd @var{standard}
747
Set television standard (NTSC, PAL (SECAM)).
748
@item -isync
749
Synchronize read on input.
750
@end table
751

    
752
@section Advanced options
753

    
754
@table @option
755
@item -map @var{input_stream_id}[:@var{sync_stream_id}]
756
Set stream mapping from input streams to output streams.
757
Just enumerate the input streams in the order you want them in the output.
758
@var{sync_stream_id} if specified sets the input stream to sync
759
against.
760
@item -map_meta_data @var{outfile}:@var{infile}
761
Set meta data information of @var{outfile} from @var{infile}.
762
@item -debug
763
Print specific debug info.
764
@item -benchmark
765
Add timings for benchmarking.
766
@item -dump
767
Dump each input packet.
768
@item -hex
769
When dumping packets, also dump the payload.
770
@item -bitexact
771
Only use bit exact algorithms (for codec testing).
772
@item -ps @var{size}
773
Set packet size in bits.
774
@item -re
775
Read input at native frame rate. Mainly used to simulate a grab device.
776
@item -loop_input
777
Loop over the input stream. Currently it works only for image
778
streams. This option is used for automatic FFserver testing.
779
@item -loop_output @var{number_of_times}
780
Repeatedly loop output for formats that support looping such as animated GIF
781
(0 will loop the output infinitely).
782
@item -threads @var{count}
783
Thread count.
784
@item -vsync @var{parameter}
785
Video sync method. Video will be stretched/squeezed to match the timestamps,
786
it is done by duplicating and dropping frames. With -map you can select from
787
which stream the timestamps should be taken. You can leave either video or
788
audio unchanged and sync the remaining stream(s) to the unchanged one.
789
@item -async @var{samples_per_second}
790
Audio sync method. "Stretches/squeezes" the audio stream to match the timestamps,
791
the parameter is the maximum samples per second by which the audio is changed.
792
-async 1 is a special case where only the start of the audio stream is corrected
793
without any later correction.
794
@item -copyts
795
Copy timestamps from input to output.
796
@item -shortest
797
Finish encoding when the shortest input stream ends.
798
@item -dts_delta_threshold
799
Timestamp discontinuity delta threshold.
800
@item -muxdelay @var{seconds}
801
Set the maximum demux-decode delay.
802
@item -muxpreload @var{seconds}
803
Set the initial demux-decode delay.
804
@end table
805

    
806
@section Preset files
807

    
808
A preset file contains a sequence of @var{option}=@var{value} pairs,
809
one for each line, specifying a sequence of options which would be
810
awkward to specify on the command line. Lines starting with the hash
811
('#') character are ignored and are used to provide comments. Check
812
the @file{ffpresets} directory in the FFmpeg source tree for examples.
813

    
814
Preset files are specified with the @code{vpre}, @code{apre} and
815
@code{spre} options. The options specified in a preset file are
816
applied to the currently selected codec of the same type as the preset
817
option.
818

    
819
The argument passed to the preset options identifies the preset file
820
to use according to the following rules.
821

    
822
First ffmpeg searches for a file named @var{arg}.ffpreset in the
823
directories @file{$HOME/.ffmpeg}, and in the datadir defined at
824
configuration time (usually @file{PREFIX/share/ffmpeg}) in that
825
order. For example, if the argument is @code{libx264-max}, it will
826
search for the file @file{libx264-max.ffpreset}.
827

    
828
If no such file is found, then ffmpeg will search for a file named
829
@var{codec_name}-@var{arg}.ffpreset in the above-mentioned
830
directories, where @var{codec_name} is the name of the codec to which
831
the preset file options will be applied. For example, if you select
832
the video codec with @code{-vcodec libx264} and use @code{-vpre max},
833
then it will search for the file @file{libx264-max.ffpreset}.
834

    
835
Finally, if the above rules failed and the argument specifies an
836
absolute pathname, ffmpeg will search for that filename. This way you
837
can specify the absolute and complete filename of the preset file, for
838
example @file{./ffpresets/libx264-max.ffpreset}.
839

    
840
@node FFmpeg formula evaluator
841
@section FFmpeg formula evaluator
842

    
843
When evaluating a rate control string, FFmpeg uses an internal formula
844
evaluator.
845

    
846
The following binary operators are available: @code{+}, @code{-},
847
@code{*}, @code{/}, @code{^}.
848

    
849
The following unary operators are available: @code{+}, @code{-},
850
@code{(...)}.
851

    
852
The following statements are available: @code{ld}, @code{st},
853
@code{while}.
854

    
855
The following functions are available:
856
@table @var
857
@item sinh(x)
858
@item cosh(x)
859
@item tanh(x)
860
@item sin(x)
861
@item cos(x)
862
@item tan(x)
863
@item atan(x)
864
@item asin(x)
865
@item acos(x)
866
@item exp(x)
867
@item log(x)
868
@item abs(x)
869
@item squish(x)
870
@item gauss(x)
871
@item mod(x, y)
872
@item max(x, y)
873
@item min(x, y)
874
@item eq(x, y)
875
@item gte(x, y)
876
@item gt(x, y)
877
@item lte(x, y)
878
@item lt(x, y)
879
@item bits2qp(bits)
880
@item qp2bits(qp)
881
@end table
882

    
883
The following constants are available:
884
@table @var
885
@item PI
886
@item E
887
@item iTex
888
@item pTex
889
@item tex
890
@item mv
891
@item fCode
892
@item iCount
893
@item mcVar
894
@item var
895
@item isI
896
@item isP
897
@item isB
898
@item avgQP
899
@item qComp
900
@item avgIITex
901
@item avgPITex
902
@item avgPPTex
903
@item avgBPTex
904
@item avgTex
905
@end table
906

    
907
@c man end
908

    
909
@ignore
910

    
911
@setfilename ffmpeg
912
@settitle FFmpeg video converter
913

    
914
@c man begin SEEALSO
915
ffserver(1), ffplay(1) and the HTML documentation of @file{ffmpeg}.
916
@c man end
917

    
918
@c man begin AUTHOR
919
Fabrice Bellard
920
@c man end
921

    
922
@end ignore
923

    
924
@section Protocols
925

    
926
The file name can be @file{-} to read from standard input or to write
927
to standard output.
928

    
929
FFmpeg also handles many protocols specified with an URL syntax.
930

    
931
Use 'ffmpeg -formats' to see a list of the supported protocols.
932

    
933
The protocol @code{http:} is currently used only to communicate with
934
FFserver (see the FFserver documentation). When FFmpeg will be a
935
video player it will also be used for streaming :-)
936

    
937
@chapter Tips
938

    
939
@itemize
940
@item For streaming at very low bitrate application, use a low frame rate
941
and a small GOP size. This is especially true for RealVideo where
942
the Linux player does not seem to be very fast, so it can miss
943
frames. An example is:
944

    
945
@example
946
ffmpeg -g 3 -r 3 -t 10 -b 50k -s qcif -f rv10 /tmp/b.rm
947
@end example
948

    
949
@item  The parameter 'q' which is displayed while encoding is the current
950
quantizer. The value 1 indicates that a very good quality could
951
be achieved. The value 31 indicates the worst quality. If q=31 appears
952
too often, it means that the encoder cannot compress enough to meet
953
your bitrate. You must either increase the bitrate, decrease the
954
frame rate or decrease the frame size.
955

    
956
@item If your computer is not fast enough, you can speed up the
957
compression at the expense of the compression ratio. You can use
958
'-me zero' to speed up motion estimation, and '-intra' to disable
959
motion estimation completely (you have only I-frames, which means it
960
is about as good as JPEG compression).
961

    
962
@item To have very low audio bitrates, reduce the sampling frequency
963
(down to 22050 Hz for MPEG audio, 22050 or 11025 for AC-3).
964

    
965
@item To have a constant quality (but a variable bitrate), use the option
966
'-qscale n' when 'n' is between 1 (excellent quality) and 31 (worst
967
quality).
968

    
969
@item When converting video files, you can use the '-sameq' option which
970
uses the same quality factor in the encoder as in the decoder.
971
It allows almost lossless encoding.
972

    
973
@end itemize
974

    
975
@bye