MOD is a format containing MPEG-2 video and AC3 audio. The extension is rarely used, that is why it can be opened only with special programs. Also MOD files can be playback by DVD players. If you want to open it with a standard player, the easiest way is to convert the file to MPG. Usually the format is used by Panasonic and JVC for recording video, the data is saved to a hard disk or SD card.

M4V is a video container that stores audio and video data used for iTunes files. Files of this type may be protected from illegal viewing and copying with Apple FairPlay DRM. In this case audio or video files should be bought in iTunes store. Not protected files can be viewed almost in any modern player because the format is based on MPEG-4 structure.