avconv: support stream specifiers in -metadata and -map_metadata

Signed-off-by: Anton Khirnov <anton@khirnov.net>

doc/avconv.texi

@@ -170,9 +170,9 @@ For example, for setting the title in the output file:
 avconv -i in.avi -metadata title="my title" out.flv
 @end example
 
-To set the language of the second stream:
+To set the language of the first audio stream:
 @example
-avconv -i INPUT -metadata:s:1 language=eng OUTPUT
+avconv -i INPUT -metadata:s:a:0 language=eng OUTPUT
 @end example
 
 @item -target @var{type} (@emph{output})
@@ -677,14 +677,28 @@ avconv -i INPUT -map 0 -map -0:a:1 OUTPUT
 
 Note that using this option disables the default mappings for this output file.
 
-@item -map_metadata[:@var{metadata_type}][:@var{index}] @var{infile}[:@var{metadata_type}][:@var{index}] (@emph{output,per-metadata})
+@item -map_metadata[:@var{metadata_spec_out}] @var{infile}[:@var{metadata_spec_in}] (@emph{output,per-metadata})
 Set metadata information of the next output file from @var{infile}. Note that
 those are file indices (zero-based), not filenames.
-Optional @var{metadata_type} parameters specify, which metadata to copy - (g)lobal
-(i.e. metadata that applies to the whole file), per-(s)tream, per-(c)hapter or
-per-(p)rogram. All metadata specifiers other than global must be followed by the
-stream/chapter/program index. If metadata specifier is omitted, it defaults to
-global.
+Optional @var{metadata_spec_in/out} parameters specify, which metadata to copy.
+A metadata specifier can have the following forms:
+@table @option
+@item @var{g}
+global metadata, i.e. metadata that applies to the whole file
+
+@item @var{s}[:@var{stream_spec}]
+per-stream metadata. @var{stream_spec} is a stream specifier as described
+in the @ref{Stream specifiers} chapter. In an input metadata specifier, the first
+matching stream is copied from. In an output metadata specifier, all matching
+streams are copied to.
+
+@item @var{c}:@var{chapter_index}
+per-chapter metadata. @var{chapter_index} is the zero-based chapter index.
+
+@item @var{p}:@var{program_index}
+per-program metadata. @var{program_index} is the zero-based program index.
+@end table
+If metadata specifier is omitted, it defaults to global.
 
 By default, global metadata is copied from the first input file,
 per-stream and per-chapter metadata is copied along with streams/chapters. These
@@ -696,6 +710,14 @@ of the output file:
 @example
 avconv -i in.ogg -map_metadata 0:s:0 out.mp3
 @end example
+
+To do the reverse, i.e. copy global metadata to all audio streams:
+@example
+avconv -i in.mkv -map_metadata:s:a 0:g out.mkv
+@end example
+Note that simple @code{0} would work as well in this example, since global
+metadata is assumed by default.
+
 @item -map_chapters @var{input_file_index} (@emph{output})
 Copy chapters from input file with index @var{input_file_index} to the next
 output file. If no chapter mapping is specified, then chapters are copied from

doc/avtools-common-opts.texi

@@ -11,6 +11,7 @@ corresponding value to true. They can be set to false by prefixing
 with "no" the option name, for example using "-nofoo" in the
 command line will set to false the boolean option with name "foo".
 
+@anchor{Stream specifiers}
 @section Stream specifiers
 Some options are applied per-stream, e.g. bitrate or codec. Stream specifiers
 are used to precisely specify which stream(s) does a given option belong to.