Handling animations efficiently

Hi there,

I am developing a platform engine in AS3 and I was wondering about handling animations. For sprite movement and what not I am using copypixels but I am more concerned about things like enviromental animations (waterfalls etc) and background animations (twinkling stars etc etc.)

Obviously, I can embed / load a .swf file for each animation, create a sprite set, or perhaps even import an flv file… My real concern is which method would be the most efficient for cpu / memory usage since I want to loads down to handle the game logic.

Any ideas would be helpful.