Just convert 'Tough' QuickTime MOV or DV files to MPEG 4 on Mac is an effective way out, for MP4 is better compatible with media players and mobile devices. However, the method will be out of operation, when move some QuickTime videos (like MOV, DV movies) to your digital player. Have downloaded a bundle of videos or music in your Mac QuickTime program, and always transfer those files to portable devices like iPad, by sync with iTunes, so you can enjoy the movies or songs on hand.
