Probably digital files on the disk, MP3's with a high encoding rate to preserve quality.
Probably also encrypted, requiring a specially provided laptop for playback.
One can "burn" audio files on DVDs. One has to have a DVD burner, but you can get one of those for $60-$100. A DVD might have 4.7 gigabytes of space where a CD only has 700 megabytes. You would have to play it on a DVD player, I guess.