doc/formats: add reference to ffmpeg(1) stream specifiers as that docs is more complete

Signed-off-by: Marton Balint <cus@passwd.hu>

doc/formats.texi

@@ -234,30 +234,10 @@ At present, applicable for MPEG-PS and MPEG-TS.
 Format stream specifiers allow selection of one or more streams that
 match specific properties.
 
-Possible forms of stream specifiers are:
-@table @option
-@item @var{stream_index}
-Matches the stream with this index.
-
-@item @var{stream_type}[:@var{stream_index}]
-@var{stream_type} is one of following: 'v' for video, 'a' for audio,
-'s' for subtitle, 'd' for data, and 't' for attachments. If
-@var{stream_index} is given, then it matches the stream number
-@var{stream_index} of this type. Otherwise, it matches all streams of
-this type.
-
-@item p:@var{program_id}[:@var{stream_index}]
-If @var{stream_index} is given, then it matches the stream with number
-@var{stream_index} in the program with the id
-@var{program_id}. Otherwise, it matches all streams in the program.
-
-@item #@var{stream_id}
-Matches the stream by a format-specific ID.
-@end table
-
 The exact semantics of stream specifiers is defined by the
 @code{avformat_match_stream_specifier()} function declared in the
-@file{libavformat/avformat.h} header.
+@file{libavformat/avformat.h} header and documented in the
+@ref{Stream specifiers,,Stream specifiers section in the ffmpeg(1) manual,ffmpeg}.
 
 @ifclear config-writeonly
 @include demuxers.texi