flv demuxer supports live rtmp inputs but there is no any info about it in the docs.

Signed-off-by: Bela Bodecs <bodecsb@vivanet.hu>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/demuxers.texi

@@ -243,11 +243,17 @@ file subdir/file-2.wav
 @end example
 @end itemize
 
-@section flv
+@section flv, live_flv
 
 Adobe Flash Video Format demuxer.
 
-This demuxer is used to demux FLV files and RTMP network streams.
+This demuxer is used to demux FLV files and RTMP network streams. In case of live network streams, if you force format, you may use live_flv option instead of flv to survive timestamp discontinuities.
+
+@example
+ffmpeg -f flv -i myfile.flv ...
+ffmpeg -f live_flv -i rtmp://<any.server>/anything/key ....
+@end example
+
 
 @table @option
 @item -flv_metadata @var{bool}