Create a low resolution second bitmap, and every few frames, copy the screen onto it (it should automatically scale down if you specify the locations on each). Save this bitmap with a number one more than the previous bitmap, as a .png or .jpg (as long as it has good compression). Then, if you have animation shop, you can just create a new animation from the set of images, or you can write a program using the animation plugin on these forums somewhere (search), that takes all the images, and creates an animation out of them.