Freezing frames on DVD Playback


I have a Sage iMac with a DVD-ROM drive and I watch DVD videos all the time, but recently I've noticed that when I wake my Mac from sleep, the DVD player app (Version 2.4) freezes every 5 to 6 seconds with the audio playing normally. The problem is fixed when I restart but I don't want to restart every time this happens. Can this be a hardware, firmware or software issue? Anybody else experiencing this or have any suggestions? :confused: