What does M4A mean?

MPEG-4 file extension used for videos downloaded from the Apple iTunes store; includes TV episodes, full-length movies, and music videos; similar to an .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."

So if you want to play M4V files freely, you need a 3rd party tool to remove the DRM, try M4V Converter PLus, it can help you.