QuickTime Player allows you to watch, create, and share movie files in Mountain Lion. To open QuickTime Player, go to the Applications folder and double-click its icon.
Playing back video and audio files
QuickTime Player can open and play back video and audio of various formats.
Video formats supported are:
QuickTime Movie (.mov extension)
MPEG-4 (.mp4 or .m4v)
Audio formats supported include:
iTunes Audio (.m4a, .m4p, and .m4b)