.M4V File Extension
What is an M4V file?
An M4V file is an MPEG-4 file used to store video downloaded from the Apple iTunes store, such as TV episodes, music videos, and full-length movies. It is similar to the .MP4 file, but may be copy-protected using Apple's FairPlay DRM copyright protection.
To play a protected M4V file, your computer must be authorized (using iTunes) with the account that was used to purchase the video. Unprotected M4V files may be recognized and played by other video players by changing the file extension from ".m4v" to ".mp4."