I don't have the game in front of me but if you go into theatre mode from the zombies menu and load up one of your recent games there's an option to create a highlight reel.
you can then customize the highlight reel and pick categories such as "best moments", etc (I forget the rest) and the number of stars.
when you generate the highlight reel it will fast forward through your game until it finds a suitable clip, record that and carry on.
I think the idea is that you eventually assemble several clips into a small video and you can pick the transitions, etc
I'm guessing it's designed for multiplayer. Seems like a great feature if your game is about 10 minutes long but trying to assemble a highlight reel from a three hour zombie game is a gruelling experience.
I found it interesting that the game seems to be using some kind of formula to automatically rate the standard of your play according to different criteria though.