Rented movie on iTunes skipping during playback

Has anyone had issues with video playback (skipping & choppy) via iTunes? I've had no problems playing DVDs or watching Netflix. But I rented a movie through iTunes the other day and it was skipping & choppy during playback. I read a few forums, which said it could be a problems with my processor, or updates to iTunes & FlashPlayer. I've done a few updates as suggested and am still having the same problems.

iTunes is not the only program having video playback issues. I was trying to make an iMovie and it is also skipping.

Lastly, when I try to play videos via QuickTime, they are just black with no audio.

I am using OS 10.8.5, but maybe I should update to Yosemite? Could it be my processor? I never had these problems in the past. My computer is only 2 years old. I am miles and miles away from an Apple store. Any feedback would be helpful!

Thanks,

Patrice

MacBook Pro, OS X Mountain Lion (10.8.5)