- audio.count: give the number of available audio track
  - audio.description(int n): give the name of the n-th audio track
  - subtitle.count: give the number of available subtitle track
  - subtitle.description(int n): give the name of the n-th subtitle track
  - subtitle.track: get and set the subtitle track to show (similar as video.subtitle)
Signed-off-by: Jean-Baptiste Kempf <jb@videolan.org>