this is a difficult problem to explain. I have encountered this on both Ubuntu and Linux Mint. I'm using the KDE CE 4 release. I tried searching the forums for a few topics, but again, this problem is difficult to describe and search for. Here's what happens: when I play a video file, there are horizontal lines that appear in certain scenes. However, if I play the file in fullscreen, this problem disappears. This isn't a problem when I watch movies and the like since they're fullscreen, but when I watch flash videos, etc it becomes a problem. I have a geforce 7600 and have used envy to install the current nvidia drivers. I'm guessing this issue is a video card issue. Also, this issue appears in all media players -- SM, M player, and Kaffeine.