Kia ora bearclaw,

I'm not a Mac user, so bear with me til someone else comes along
You could try VLC player. It's free, has codecs installed & plays most file types. You'll find a link for download, plus more info within the link below.
CODECs list for Movies /Alternate players / Video help forums

Always check a movie file with Bitzi before download. Bitzi's a site where users can rate files...you'll get some idea of the file's content & quality. It's good for weeding out the misnamed crap. If a movie's not rated but you want to chance it, then preview after ~15% download. If a file has heaps of sources but no Bitzi rating, chances are it's a fake.
How to use Bitzi