Me and Lauren wanted to watch the Legend of Korra on her MacBook that was linked to our tv, but we couldn’t play it because the file was in MKV format. QuickTime doesn’t natively support MKV files and installing a DivX player didn’t help either. DivX player did playback the video, but there was no audio and it kept showing a message about an AC83 decoder being missing. Perian, on the other hand, is a powerful QuickTime extension, which allows playback of video AND audio without any problems. So download Perian for all your video playback needs on your OSX!