Specification updates

Following discussions on our mailing list to better support the Opus codec, we added some elements to Matroska v4:

  • CodecDelay to specify the internal delay of a codec that needs to be applied to each timestamp
  • DiscardPadding some padding added to a frame (mostly audio) that should not be played (for sample accurate gapless playback)
  • SeekPreRoll a value that must be removed from the timecode of a track for proper seeking

libmatroska and libmatroska2 have been updated accordingly on GitHub, as well as the XML file used to generate the specs and the libs.