The main reason for pixelation (picture break up) on playback is contamination of the disc. Scratches, thumbprints, food, fluid and various other substances may be present on the disc and these will prevent the laser pick up from retrieving the information.

Gently wipe the surface in an outwards motion with a clean non abrasive cloth. You should remember that dvd discs are not as resilient and robust as CDs and thus should be treated with care. The second reason for pixelation will be contamination of the laser pick up.

Good practice suggests that you should really invest in a dvd lens cleaner and use this every couple of months. This will prolong the life of your dvd player and maintain  the same high quality playback as when you originally purchased the machine.