Uneven video playback

Ever since I have installed Ubuntu 8.04, all of my videos playback have this line going across the screen. It appears as if the video above this line has moved over to the left or right from the video below the line to make it look offset. This slowly creeps upward as I watch the video. Is there a plug in or something missing that can cause this?

I finally figured out what was causing my problem and took care of it. Thanks to those who just looked in.