Currently, the matroska default flag is parsed in matroska-demux.c under the add stream function. However, it remains unused. It should be used to determine which video/audio/subtitle track should be displayed as they were intended by the mkv creator.

This is particularly useful for example playback of english video with optional english subtitles. In this case the subtitles which has a default track flag of 0 should not be displayed at all but made available to be accessed by clients.

Incidentally, which audio/subtitle stream gst plays when using playbin seems indeterminate, with different streams playing by default at random for each reset (as seen on totem 2.30.2). This would be fixed more or less by the above enhancement.