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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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@include fftools-common-opts.texi
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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 (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
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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.
627
The alternative is to deinterlace the input stream with
628
@option{-deinterlace}, but deinterlacing introduces losses.
629
@item -psnr
630
Calculate PSNR of compressed frames.
631
@item -vstats
632
Dump video coding statistics to @file{vstats_HHMMSS.log}.
633
@item -vstats_file @var{file}
634
Dump video coding statistics to @var{file}.
635
@item -top @var{n}
636
top=1/bottom=0/auto=-1 field first
637
@item -dc @var{precision}
638
Intra_dc_precision.
639
@item -vtag @var{fourcc/tag}
640
Force video tag/fourcc.
641
@item -qphist
642
Show QP histogram.
643
@item -vbsf @var{bitstream_filter}
644
Bitstream filters available are "dump_extra", "remove_extra", "noise", "h264_mp4toannexb", "imxdump", "mjpegadump".
645
@example
646
ffmpeg -i h264.mp4 -vcodec copy -vbsf h264_mp4toannexb -an out.h264
647
@end example
648
@end table
649

    
650
@section Audio Options
651

    
652
@table @option
653
@item -aframes @var{number}
654
Set the number of audio frames to record.
655
@item -ar @var{freq}
656
Set the audio sampling frequency (default = 44100 Hz).
657
@item -ab @var{bitrate}
658
Set the audio bitrate in bit/s (default = 64k).
659
@item -ac @var{channels}
660
Set the number of audio channels (default = 1).
661
@item -an
662
Disable audio recording.
663
@item -acodec @var{codec}
664
Force audio codec to @var{codec}. Use the @code{copy} special value to
665
specify that the raw codec data must be copied as is.
666
@item -newaudio
667
Add a new audio track to the output file. If you want to specify parameters,
668
do so before @code{-newaudio} (@code{-acodec}, @code{-ab}, etc..).
669

    
670
Mapping will be done automatically, if the number of output streams is equal to
671
the number of input streams, else it will pick the first one that matches. You
672
can override the mapping using @code{-map} as usual.
673

    
674
Example:
675
@example
676
ffmpeg -i file.mpg -vcodec copy -acodec ac3 -ab 384k test.mpg -acodec mp2 -ab 192k -newaudio
677
@end example
678
@item -alang @var{code}
679
Set the ISO 639 language code (3 letters) of the current audio stream.
680
@end table
681

    
682
@section Advanced Audio options:
683

    
684
@table @option
685
@item -atag @var{fourcc/tag}
686
Force audio tag/fourcc.
687
@item -absf @var{bitstream_filter}
688
Bitstream filters available are "dump_extra", "remove_extra", "noise", "mp3comp", "mp3decomp".
689
@end table
690

    
691
@section Subtitle options:
692

    
693
@table @option
694
@item -scodec @var{codec}
695
Force subtitle codec ('copy' to copy stream).
696
@item -newsubtitle
697
Add a new subtitle stream to the current output stream.
698
@item -slang @var{code}
699
Set the ISO 639 language code (3 letters) of the current subtitle stream.
700
@item -sn
701
Disable subtitle recording.
702
@item -sbsf @var{bitstream_filter}
703
Bitstream filters available are "mov2textsub", "text2movsub".
704
@example
705
ffmpeg -i file.mov -an -vn -sbsf mov2textsub -scodec copy -f rawvideo sub.txt
706
@end example
707
@end table
708

    
709
@section Audio/Video grab options
710

    
711
@table @option
712
@item -vc @var{channel}
713
Set video grab channel (DV1394 only).
714
@item -tvstd @var{standard}
715
Set television standard (NTSC, PAL (SECAM)).
716
@item -isync
717
Synchronize read on input.
718
@end table
719

    
720
@section Advanced options
721

    
722
@table @option
723
@item -map @var{input_stream_id}[:@var{sync_stream_id}]
724
Set stream mapping from input streams to output streams.
725
Just enumerate the input streams in the order you want them in the output.
726
@var{sync_stream_id} if specified sets the input stream to sync
727
against.
728
@item -map_meta_data @var{outfile}:@var{infile}
729
Set meta data information of @var{outfile} from @var{infile}.
730
@item -debug
731
Print specific debug info.
732
@item -benchmark
733
Add timings for benchmarking.
734
@item -dump
735
Dump each input packet.
736
@item -hex
737
When dumping packets, also dump the payload.
738
@item -bitexact
739
Only use bit exact algorithms (for codec testing).
740
@item -ps @var{size}
741
Set RTP payload size in bytes.
742
@item -re
743
Read input at native frame rate. Mainly used to simulate a grab device.
744
@item -loop_input
745
Loop over the input stream. Currently it works only for image
746
streams. This option is used for automatic FFserver testing.
747
@item -loop_output @var{number_of_times}
748
Repeatedly loop output for formats that support looping such as animated GIF
749
(0 will loop the output infinitely).
750
@item -threads @var{count}
751
Thread count.
752
@item -vsync @var{parameter}
753
Video sync method. Video will be stretched/squeezed to match the timestamps,
754
it is done by duplicating and dropping frames. With -map you can select from
755
which stream the timestamps should be taken. You can leave either video or
756
audio unchanged and sync the remaining stream(s) to the unchanged one.
757
@item -async @var{samples_per_second}
758
Audio sync method. "Stretches/squeezes" the audio stream to match the timestamps,
759
the parameter is the maximum samples per second by which the audio is changed.
760
-async 1 is a special case where only the start of the audio stream is corrected
761
without any later correction.
762
@item -copyts
763
Copy timestamps from input to output.
764
@item -shortest
765
Finish encoding when the shortest input stream ends.
766
@item -dts_delta_threshold
767
Timestamp discontinuity delta threshold.
768
@item -muxdelay @var{seconds}
769
Set the maximum demux-decode delay.
770
@item -muxpreload @var{seconds}
771
Set the initial demux-decode delay.
772
@end table
773

    
774
@section Preset files
775

    
776
A preset file contains a sequence of @var{option}=@var{value} pairs,
777
one for each line, specifying a sequence of options which would be
778
awkward to specify on the command line. Lines starting with the hash
779
('#') character are ignored and are used to provide comments. Check
780
the @file{ffpresets} directory in the FFmpeg source tree for examples.
781

    
782
Preset files are specified with the @code{vpre}, @code{apre},
783
@code{spre}, and @code{fpre} options. The @code{fpre} option takes the
784
filename of the preset instead of a preset name as input and can be
785
used for any kind of codec. For the @code{vpre}, @code{apre}, and
786
@code{spre} options, the options specified in a preset file are
787
applied to the currently selected codec of the same type as the preset
788
option.
789

    
790
The argument passed to the @code{vpre}, @code{apre}, and @code{spre}
791
preset options identifies the preset file to use according to the
792
following rules:
793

    
794
First ffmpeg searches for a file named @var{arg}.ffpreset in the
795
directories @file{$HOME/.ffmpeg}, and in the datadir defined at
796
configuration time (usually @file{PREFIX/share/ffmpeg}) in that
797
order. For example, if the argument is @code{libx264-max}, it will
798
search for the file @file{libx264-max.ffpreset}.
799

    
800
If no such file is found, then ffmpeg will search for a file named
801
@var{codec_name}-@var{arg}.ffpreset in the above-mentioned
802
directories, where @var{codec_name} is the name of the codec to which
803
the preset file options will be applied. For example, if you select
804
the video codec with @code{-vcodec libx264} and use @code{-vpre max},
805
then it will search for the file @file{libx264-max.ffpreset}.
806

    
807
@anchor{FFmpeg formula evaluator}
808
@section FFmpeg formula evaluator
809

    
810
When evaluating a rate control string, FFmpeg uses an internal formula
811
evaluator.
812

    
813
The following binary operators are available: @code{+}, @code{-},
814
@code{*}, @code{/}, @code{^}.
815

    
816
The following unary operators are available: @code{+}, @code{-},
817
@code{(...)}.
818

    
819
The following statements are available: @code{ld}, @code{st},
820
@code{while}.
821

    
822
The following functions are available:
823
@table @var
824
@item sinh(x)
825
@item cosh(x)
826
@item tanh(x)
827
@item sin(x)
828
@item cos(x)
829
@item tan(x)
830
@item atan(x)
831
@item asin(x)
832
@item acos(x)
833
@item exp(x)
834
@item log(x)
835
@item abs(x)
836
@item squish(x)
837
@item gauss(x)
838
@item mod(x, y)
839
@item max(x, y)
840
@item min(x, y)
841
@item eq(x, y)
842
@item gte(x, y)
843
@item gt(x, y)
844
@item lte(x, y)
845
@item lt(x, y)
846
@item bits2qp(bits)
847
@item qp2bits(qp)
848
@end table
849

    
850
The following constants are available:
851
@table @var
852
@item PI
853
@item E
854
@item iTex
855
@item pTex
856
@item tex
857
@item mv
858
@item fCode
859
@item iCount
860
@item mcVar
861
@item var
862
@item isI
863
@item isP
864
@item isB
865
@item avgQP
866
@item qComp
867
@item avgIITex
868
@item avgPITex
869
@item avgPPTex
870
@item avgBPTex
871
@item avgTex
872
@end table
873

    
874
@c man end
875

    
876
@ignore
877

    
878
@setfilename ffmpeg
879
@settitle FFmpeg video converter
880

    
881
@c man begin SEEALSO
882
ffserver(1), ffplay(1) and the HTML documentation of @file{ffmpeg}.
883
@c man end
884

    
885
@c man begin AUTHOR
886
Fabrice Bellard
887
@c man end
888

    
889
@end ignore
890

    
891
@section Protocols
892

    
893
The file name can be @file{-} to read from standard input or to write
894
to standard output.
895

    
896
FFmpeg also handles many protocols specified with an URL syntax.
897

    
898
Use 'ffmpeg -protocols' to see a list of the supported protocols.
899

    
900
The protocol @code{http:} is currently used only to communicate with
901
FFserver (see the FFserver documentation). When FFmpeg will be a
902
video player it will also be used for streaming :-)
903

    
904
@chapter Tips
905

    
906
@itemize
907
@item For streaming at very low bitrate application, use a low frame rate
908
and a small GOP size. This is especially true for RealVideo where
909
the Linux player does not seem to be very fast, so it can miss
910
frames. An example is:
911

    
912
@example
913
ffmpeg -g 3 -r 3 -t 10 -b 50k -s qcif -f rv10 /tmp/b.rm
914
@end example
915

    
916
@item  The parameter 'q' which is displayed while encoding is the current
917
quantizer. The value 1 indicates that a very good quality could
918
be achieved. The value 31 indicates the worst quality. If q=31 appears
919
too often, it means that the encoder cannot compress enough to meet
920
your bitrate. You must either increase the bitrate, decrease the
921
frame rate or decrease the frame size.
922

    
923
@item If your computer is not fast enough, you can speed up the
924
compression at the expense of the compression ratio. You can use
925
'-me zero' to speed up motion estimation, and '-intra' to disable
926
motion estimation completely (you have only I-frames, which means it
927
is about as good as JPEG compression).
928

    
929
@item To have very low audio bitrates, reduce the sampling frequency
930
(down to 22050 Hz for MPEG audio, 22050 or 11025 for AC-3).
931

    
932
@item To have a constant quality (but a variable bitrate), use the option
933
'-qscale n' when 'n' is between 1 (excellent quality) and 31 (worst
934
quality).
935

    
936
@item When converting video files, you can use the '-sameq' option which
937
uses the same quality factor in the encoder as in the decoder.
938
It allows almost lossless encoding.
939

    
940
@end itemize
941

    
942
@bye