The M4V - iTunes Video File is a file extension that is used to facilitate the play of videos that have been downloaded from the Apple iTunes store. The videos that are compatible with this file extension includes TV episodes, full-length movies, as well as music videos. The M4V file is almost identical to an MP4 file, with the exception being that M4V files can be copy-protected by Apple’ FairPlay DRM copyright protection. In order for your computer or device to play a copyrighted M4V file it must be authorized through iTunes with the account that the video was purchased through.
When the M4V file is unprotected, it can played by changing the file extension to MP4.