Add muxers.texi file.

Signed-off-by: Janne Grunau <janne-ffmpeg@jannau.net>
(cherry picked from commit 85466e1e)

doc/ffmpeg.texi

@@ -977,6 +977,7 @@ file to which you want to add them.
 
 @include eval.texi
 @include demuxers.texi
+@include muxers.texi
 @include indevs.texi
 @include outdevs.texi
 @include protocols.texi

doc/ffplay.texi

@@ -155,6 +155,7 @@ Seek to percentage in file corresponding to fraction of width.
 
 @include eval.texi
 @include demuxers.texi
+@include muxers.texi
 @include indevs.texi
 @include outdevs.texi
 @include protocols.texi

doc/ffprobe.texi

@@ -110,6 +110,7 @@ with name "STREAM".
 @c man end
 
 @include demuxers.texi
+@include muxers.texi
 @include protocols.texi
 @include indevs.texi
 

doc/muxers.texi

+@chapter Muxers
+@c man begin MUXERS
+
+Muxers are configured elements in FFmpeg which allow writing
+multimedia streams to a particular type of file.
+
+When you configure your FFmpeg build, all the supported muxers
+are enabled by default. You can list all available muxers using the
+configure option @code{--list-muxers}.
+
+You can disable all the muxers with the configure option
+@code{--disable-muxers} and selectively enable / disable single muxers
+with the options @code{--enable-muxer=@var{MUXER}} /
+@code{--disable-muxer=@var{MUXER}}.
+
+The option @code{-formats} of the ff* tools will display the list of
+enabled muxers.
+
+A description of some of the currently available muxers follows.
+
+@c man end MUXERS