Some Playstation 1 games played music in normal CD players!

While CD players may be going the way of tape players as MP3 files take over, at the time of the first Playstation game, they were still widely popular.

Game developers would often format the game disc to play in-game audio on a regular CD player. Not sure why you would want to listen to the oft-repetitive music just for fun, but to each their own.

Perhaps because developers would sometimes add hidden tracks that could not be heard while playing the game but could be accessed when the disc was played on a CD player.

Unlike regular audio CDs though, these game discs would have tracks of just silence and the first track was often just scrambled sounds.

(Source)