I am trying to find this as well.
While Echo does something useful it is not what i am looking for actually. Or does it?
Lets say I have footage shot in 12fps for creating time-lapse out of it. I am going to speed the footage up that these 12 frames will make up 1 frame. I want to average these frames to reduce noise and create fluid motion.
It could be done with the tools in AE I am sure.