AUDIO_TS is for compatibility with future "universal" DVD players that can play both DVD-Video and DVD-Audio. A DVD-Audio disc will use the AUDIO_TS audio title set. DVD-Audio disks are presumably better than CD-Audio discs and may replace them some day. And possibly "universal" DVDs will be produced that contain both DVD-Video and DVD-Audio material. At the present time DVD-Audio is a little ahead of its time, in that its audio quality is higher than most systems can reproduce and DVD-Audio players aren't in the stores. At least, that is my understanding.