Keyframing (whether it be for position, size and/or plugin attributes) is such a fundamental concept in video editing that I respectfully suggest you spend some 'real time' with your user manual and read up on it. I could explain the concepts but it's an essay that is rather too long for me to do justice to in a forum post.


AE = Adobe After Effects. Might be new version 7 features but it contains some nice 'tracking' features that would do this for you pretty much automagically.