ffmpeg source update for sep 09

source/patched-ffmpeg-mt/doc/ffmpeg-doc.texi

 \input texinfo @c -*- texinfo -*-
 
 @settitle FFmpeg Documentation
 @titlepage
 @sp 7
 @center @titlefont{FFmpeg Documentation}
 @sp 3
 @end titlepage
 
 @chapter Synopsis
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 @table @option
 @item -aframes @var{number}
 Set the number of audio frames to record.
 @item -ar @var{freq}
 Set the audio sampling frequency (default = 44100 Hz).
 @item -ab @var{bitrate}
 Set the audio bitrate in bit/s (default = 64k).
 @item -aq @var{q}
 Set the audio quality (codec-specific, VBR).
 @item -ac @var{channels}
-Set the number of audio channels (default = 1).
+Set the number of audio channels. For input streams it is set by
+default to 1, for output streams it is set by default to the same
+number of audio channels in input. If the input file has audio streams
+with different channel count, the behaviour is undefined.
 @item -an
 Disable audio recording.
 @item -acodec @var{codec}
 Force audio codec to @var{codec}. Use the @code{copy} special value to
 specify that the raw codec data must be copied as is.
 @item -newaudio
 Add a new audio track to the output file. If you want to specify parameters,
 do so before @code{-newaudio} (@code{-acodec}, @code{-ab}, etc..).
 
 Mapping will be done automatically, if the number of output streams is equal to
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 ffplay(1), ffprobe(1), ffserver(1) and the FFmpeg HTML documentation
 @c man end
 
 @c man begin AUTHORS
 The FFmpeg developers
 @c man end
 
 @end ignore
 
 @bye