Haven't used my DVD player in a long time, decided to play a newly acquired Movie and it kept popping back out - so I tried a dozen more, same symptoms. I popped in a Music CD and it plays - whats wrong?? I use Quicktime, VLC, and DVD Player.
You didn't identify your Mac but what you described is a common symptom of a Mac slot loading drive not working right. It's not unusual for a DVD to work OK but a CD not work and vice versa. Buy a can of compressed air and blow several short blasts into the drive slot to see if that restores it to working for both DVDs and CDs.