Cows: footage for animated background

Originally, for the cow in my animation, I was just going to chop up some photos of a toy cow and make puppets similar to the ones I've already done. After seeing how much they cost I soon changed my mind!

I then thought that, seeing as we need to have at least one animated backdrop in our animation, it would make more sense to go out and film a cow that I would then be able to use in the background. As a result I spent most of this weekend out shooting some footage.

I ended up shooting a lot more footage than this (almost 1GB in total) but decided against uploading all of it! I've sifted through all my clips and picked out the sections that I think I can use:

My camera's not terribly hi-res, but seeing as the cows will be fairly small I'm hoping it won't be too much of a problem.

I'm hoping to cut the cow out of the background and composite it over the field beyond the window in the background of my animation. I'm planning on experimenting with After Effects' "Roto Brush" tool that I've heard very good things about. From what I understand so far it's a slightly more automated rotoscoping process that allows you to quickly cut parts of footage out from the background. It sounds like a very versatile tool and I'm hoping that there's enough distinction between the cows and the background for me to cut them out effectively.

(No practical use whatsoever, but I thought it was funny!)