How to blur edges of green screen footage (png sequences)

I swear that someone can help me with this. I’m looking for a method to blur the edges of a pre-keyed png sequence. I know that someone (also my self) uses the dithertemporalAA material function to archive something close, but personally i’m not satisfyed at all using this method, so i’m looking for an alternative that gives me a better result for integrating better the keyed out footage with 3d environment. Thank you for your help.