Add a second metadata compatibility layer, so that metadata that gets

demuxed with new API is automatically converted to the old API,
allowing old applications to stay functional.

Originally committed as revision 16499 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavformat/metadata.h

@@ -36,6 +36,7 @@ struct AVMetadata{
 };
 
 #if LIBAVFORMAT_VERSION_MAJOR < 53
+void ff_metadata_demux_compat(AVFormatContext *s);
 void ff_metadata_sync_compat(AVFormatContext *s);
 #endif