What's the problem with it being slow ? I mean, it's not like if you were playing the game, you're supposed to already have recorded the .rec movie file, and you can convert it into an avi file whenever you have some time, you don't even have to stay in front of your computer during that operation.
Oh and if you're wondering about speed of the resulting avi file, it won't affect it : even if it's encoding the avi file at 2 fps, when you will watch the avi file in your favorite media player it will still have 60 images per second.