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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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@include fftools-common-opts.texi
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@section Main options
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@table @option
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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 -timestamp @var{time}
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Set the timestamp.
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@item -metadata @var{key}=@var{value}
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Set a metadata key/value pair.
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For example, for setting the title in the output file:
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@example
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ffmpeg -i in.avi -metadata title="my title" out.flv
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@end example
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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 16cif
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1408x1152
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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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@item -vlang @var{code}
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Set the ISO 639 language code (3 letters) of the current video 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.
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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
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FF_MB_DECISION_RD: rate distortion
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@end table
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@item -4mv
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Use four motion vector by macroblock (MPEG-4 only).
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@item -part
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Use data partitioning (MPEG-4 only).
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@item -bug @var{param}
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Work around encoder bugs that are not auto-detected.
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@item -strict @var{strictness}
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How strictly to follow the standards.
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@item -aic
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Enable Advanced intra coding (h263+).
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@item -umv
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Enable Unlimited Motion Vector (h263+)
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@item -deinterlace
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Deinterlace pictures.
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@item -ilme
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Force interlacing support in encoder (MPEG-2 and MPEG-4 only).
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Use this option if your input file is interlaced and you want
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to keep the interlaced format for minimum losses.
629
The alternative is to deinterlace the input stream with
630
@option{-deinterlace}, but deinterlacing introduces losses.
631
@item -psnr
632
Calculate PSNR of compressed frames.
633
@item -vstats
634
Dump video coding statistics to @file{vstats_HHMMSS.log}.
635
@item -vstats_file @var{file}
636
Dump video coding statistics to @var{file}.
637
@item -top @var{n}
638
top=1/bottom=0/auto=-1 field first
639
@item -dc @var{precision}
640
Intra_dc_precision.
641
@item -vtag @var{fourcc/tag}
642
Force video tag/fourcc.
643
@item -qphist
644
Show QP histogram.
645
@item -vbsf @var{bitstream_filter}
646
Bitstream filters available are "dump_extra", "remove_extra", "noise", "h264_mp4toannexb", "imxdump", "mjpegadump".
647
@example
648
ffmpeg -i h264.mp4 -vcodec copy -vbsf h264_mp4toannexb -an out.h264
649
@end example
650
@end table
651

    
652
@section Audio Options
653

    
654
@table @option
655
@item -aframes @var{number}
656
Set the number of audio frames to record.
657
@item -ar @var{freq}
658
Set the audio sampling frequency (default = 44100 Hz).
659
@item -ab @var{bitrate}
660
Set the audio bitrate in bit/s (default = 64k).
661
@item -aq @var{q}
662
Set the audio quality (codec-specific, VBR).
663
@item -ac @var{channels}
664
Set the number of audio channels (default = 1).
665
@item -an
666
Disable audio recording.
667
@item -acodec @var{codec}
668
Force audio codec to @var{codec}. Use the @code{copy} special value to
669
specify that the raw codec data must be copied as is.
670
@item -newaudio
671
Add a new audio track to the output file. If you want to specify parameters,
672
do so before @code{-newaudio} (@code{-acodec}, @code{-ab}, etc..).
673

    
674
Mapping will be done automatically, if the number of output streams is equal to
675
the number of input streams, else it will pick the first one that matches. You
676
can override the mapping using @code{-map} as usual.
677

    
678
Example:
679
@example
680
ffmpeg -i file.mpg -vcodec copy -acodec ac3 -ab 384k test.mpg -acodec mp2 -ab 192k -newaudio
681
@end example
682
@item -alang @var{code}
683
Set the ISO 639 language code (3 letters) of the current audio stream.
684
@end table
685

    
686
@section Advanced Audio options:
687

    
688
@table @option
689
@item -atag @var{fourcc/tag}
690
Force audio tag/fourcc.
691
@item -absf @var{bitstream_filter}
692
Bitstream filters available are "dump_extra", "remove_extra", "noise", "mp3comp", "mp3decomp".
693
@end table
694

    
695
@section Subtitle options:
696

    
697
@table @option
698
@item -scodec @var{codec}
699
Force subtitle codec ('copy' to copy stream).
700
@item -newsubtitle
701
Add a new subtitle stream to the current output stream.
702
@item -slang @var{code}
703
Set the ISO 639 language code (3 letters) of the current subtitle stream.
704
@item -sn
705
Disable subtitle recording.
706
@item -sbsf @var{bitstream_filter}
707
Bitstream filters available are "mov2textsub", "text2movsub".
708
@example
709
ffmpeg -i file.mov -an -vn -sbsf mov2textsub -scodec copy -f rawvideo sub.txt
710
@end example
711
@end table
712

    
713
@section Audio/Video grab options
714

    
715
@table @option
716
@item -vc @var{channel}
717
Set video grab channel (DV1394 only).
718
@item -tvstd @var{standard}
719
Set television standard (NTSC, PAL (SECAM)).
720
@item -isync
721
Synchronize read on input.
722
@end table
723

    
724
@section Advanced options
725

    
726
@table @option
727
@item -map @var{input_stream_id}[:@var{sync_stream_id}]
728
Set stream mapping from input streams to output streams.
729
Just enumerate the input streams in the order you want them in the output.
730
@var{sync_stream_id} if specified sets the input stream to sync
731
against.
732
@item -map_meta_data @var{outfile}:@var{infile}
733
Set meta data information of @var{outfile} from @var{infile}.
734
@item -debug
735
Print specific debug info.
736
@item -benchmark
737
Show benchmarking information at the end of an encode.
738
Shows CPU time used and maximum memory consumption.
739
Maximum memory consumption is not supported on all systems,
740
it will usually display as 0 if not supported.
741
@item -dump
742
Dump each input packet.
743
@item -hex
744
When dumping packets, also dump the payload.
745
@item -bitexact
746
Only use bit exact algorithms (for codec testing).
747
@item -ps @var{size}
748
Set RTP payload size in bytes.
749
@item -re
750
Read input at native frame rate. Mainly used to simulate a grab device.
751
@item -loop_input
752
Loop over the input stream. Currently it works only for image
753
streams. This option is used for automatic FFserver testing.
754
@item -loop_output @var{number_of_times}
755
Repeatedly loop output for formats that support looping such as animated GIF
756
(0 will loop the output infinitely).
757
@item -threads @var{count}
758
Thread count.
759
@item -vsync @var{parameter}
760
Video sync method. Video will be stretched/squeezed to match the timestamps,
761
it is done by duplicating and dropping frames. With -map you can select from
762
which stream the timestamps should be taken. You can leave either video or
763
audio unchanged and sync the remaining stream(s) to the unchanged one.
764
@item -async @var{samples_per_second}
765
Audio sync method. "Stretches/squeezes" the audio stream to match the timestamps,
766
the parameter is the maximum samples per second by which the audio is changed.
767
-async 1 is a special case where only the start of the audio stream is corrected
768
without any later correction.
769
@item -copyts
770
Copy timestamps from input to output.
771
@item -shortest
772
Finish encoding when the shortest input stream ends.
773
@item -dts_delta_threshold
774
Timestamp discontinuity delta threshold.
775
@item -muxdelay @var{seconds}
776
Set the maximum demux-decode delay.
777
@item -muxpreload @var{seconds}
778
Set the initial demux-decode delay.
779
@end table
780

    
781
@section Preset files
782

    
783
A preset file contains a sequence of @var{option}=@var{value} pairs,
784
one for each line, specifying a sequence of options which would be
785
awkward to specify on the command line. Lines starting with the hash
786
('#') character are ignored and are used to provide comments. Check
787
the @file{ffpresets} directory in the FFmpeg source tree for examples.
788

    
789
Preset files are specified with the @code{vpre}, @code{apre},
790
@code{spre}, and @code{fpre} options. The @code{fpre} option takes the
791
filename of the preset instead of a preset name as input and can be
792
used for any kind of codec. For the @code{vpre}, @code{apre}, and
793
@code{spre} options, the options specified in a preset file are
794
applied to the currently selected codec of the same type as the preset
795
option.
796

    
797
The argument passed to the @code{vpre}, @code{apre}, and @code{spre}
798
preset options identifies the preset file to use according to the
799
following rules:
800

    
801
First ffmpeg searches for a file named @var{arg}.ffpreset in the
802
directories @file{$HOME/.ffmpeg}, and in the datadir defined at
803
configuration time (usually @file{PREFIX/share/ffmpeg}) in that
804
order. For example, if the argument is @code{libx264-max}, it will
805
search for the file @file{libx264-max.ffpreset}.
806

    
807
If no such file is found, then ffmpeg will search for a file named
808
@var{codec_name}-@var{arg}.ffpreset in the above-mentioned
809
directories, where @var{codec_name} is the name of the codec to which
810
the preset file options will be applied. For example, if you select
811
the video codec with @code{-vcodec libx264} and use @code{-vpre max},
812
then it will search for the file @file{libx264-max.ffpreset}.
813

    
814
@anchor{FFmpeg formula evaluator}
815
@section FFmpeg formula evaluator
816

    
817
When evaluating a rate control string, FFmpeg uses an internal formula
818
evaluator.
819

    
820
The following binary operators are available: @code{+}, @code{-},
821
@code{*}, @code{/}, @code{^}.
822

    
823
The following unary operators are available: @code{+}, @code{-},
824
@code{(...)}.
825

    
826
The following statements are available: @code{ld}, @code{st},
827
@code{while}.
828

    
829
The following functions are available:
830
@table @var
831
@item sinh(x)
832
@item cosh(x)
833
@item tanh(x)
834
@item sin(x)
835
@item cos(x)
836
@item tan(x)
837
@item atan(x)
838
@item asin(x)
839
@item acos(x)
840
@item exp(x)
841
@item log(x)
842
@item abs(x)
843
@item squish(x)
844
@item gauss(x)
845
@item mod(x, y)
846
@item max(x, y)
847
@item min(x, y)
848
@item eq(x, y)
849
@item gte(x, y)
850
@item gt(x, y)
851
@item lte(x, y)
852
@item lt(x, y)
853
@item bits2qp(bits)
854
@item qp2bits(qp)
855
@end table
856

    
857
The following constants are available:
858
@table @var
859
@item PI
860
@item E
861
@item iTex
862
@item pTex
863
@item tex
864
@item mv
865
@item fCode
866
@item iCount
867
@item mcVar
868
@item var
869
@item isI
870
@item isP
871
@item isB
872
@item avgQP
873
@item qComp
874
@item avgIITex
875
@item avgPITex
876
@item avgPPTex
877
@item avgBPTex
878
@item avgTex
879
@end table
880

    
881
@c man end
882

    
883
@ignore
884

    
885
@setfilename ffmpeg
886
@settitle FFmpeg video converter
887

    
888
@c man begin SEEALSO
889
ffserver(1), ffplay(1) and the HTML documentation of @file{ffmpeg}.
890
@c man end
891

    
892
@c man begin AUTHOR
893
Fabrice Bellard
894
@c man end
895

    
896
@end ignore
897

    
898
@section Protocols
899

    
900
The file name can be @file{-} to read from standard input or to write
901
to standard output.
902

    
903
FFmpeg also handles many protocols specified with an URL syntax.
904

    
905
Use 'ffmpeg -protocols' to see a list of the supported protocols.
906

    
907
The protocol @code{http:} is currently used only to communicate with
908
FFserver (see the FFserver documentation). When FFmpeg will be a
909
video player it will also be used for streaming :-)
910

    
911
@chapter Tips
912

    
913
@itemize
914
@item For streaming at very low bitrate application, use a low frame rate
915
and a small GOP size. This is especially true for RealVideo where
916
the Linux player does not seem to be very fast, so it can miss
917
frames. An example is:
918

    
919
@example
920
ffmpeg -g 3 -r 3 -t 10 -b 50k -s qcif -f rv10 /tmp/b.rm
921
@end example
922

    
923
@item  The parameter 'q' which is displayed while encoding is the current
924
quantizer. The value 1 indicates that a very good quality could
925
be achieved. The value 31 indicates the worst quality. If q=31 appears
926
too often, it means that the encoder cannot compress enough to meet
927
your bitrate. You must either increase the bitrate, decrease the
928
frame rate or decrease the frame size.
929

    
930
@item If your computer is not fast enough, you can speed up the
931
compression at the expense of the compression ratio. You can use
932
'-me zero' to speed up motion estimation, and '-intra' to disable
933
motion estimation completely (you have only I-frames, which means it
934
is about as good as JPEG compression).
935

    
936
@item To have very low audio bitrates, reduce the sampling frequency
937
(down to 22050 Hz for MPEG audio, 22050 or 11025 for AC-3).
938

    
939
@item To have a constant quality (but a variable bitrate), use the option
940
'-qscale n' when 'n' is between 1 (excellent quality) and 31 (worst
941
quality).
942

    
943
@item When converting video files, you can use the '-sameq' option which
944
uses the same quality factor in the encoder as in the decoder.
945
It allows almost lossless encoding.
946

    
947
@end itemize
948

    
949
@bye