That happens when a video isn't the same proportions as your screen. If you have widescreen, regular TV doesn't use the entire screen and if you have standard TV, then widescreen video won't use the top and bottom. It's an inevitable consequence of the fact that we have different aspect ratios for old TV, HDTV and movies (which have a bunch of aspect ratios). If you zoom the picture it will either distort the image or cut off part of it. Can't be avoided.