Play all kind of videos with Perian
Mac OS X uses QuickTime as the standard for everything in connection with video (file extension: .mov). However, there are situations, when you receive video files that have a different file format and thus can not be played with the standard setup of Mac OS X.
This is exactly where Perian comes in. It’s a free addition to the QuickTime Player, that enables you to watch all kinds of video and audio file types on your Mac using QuickTime Player.
It adds native support for a long list of file types, so you can play them as they were QuickTime files, or e.g. use them in iLife programs.
Great, huh? Go get it at www.perian.org