DVD player v5.4.2 failure

My DVD player application (v 5.4.2) launches when I insert a DVD, but fails to recognize the DVD and play it. I have a MacBook Pro, running OS X v10.6.8. The failure occurred slowly. Over the course of weeks/months, the DVD player changed from playing DVDs correctly to requiring me to open media and select the DVD, then select the Video folder, in order to function. The DVD reader still works for audio discs; iTunes launches normally. I can also read non-video, information discs. Please Advise.