I'm just trying a little experiment and I simply can't seem to get this to work!
What I'm trying to achieve is a moving 'trail' behind an actor dancing across the screen. This is black and white, character against a black background (so can be luma keyed etc). Basically rather than having a smooth video movement I'm taking the footage at around 200/sec shutter speed so that I get clear concise frames, then I'm taking every fifth frame or so (using Posterize time), having done this I'm trying to get an echo of the previous, say, two or three frames. I want these to be faded, as the actor moves to a new frame the last one should fade out as the new one fade in.
The effect I'm imagining is something like a trail of previous frames that fades gently out at the end.
I've tried mucking about with echo but that just kinda cuts-to the next frame rather than fading out. I tried multiple layers, each a step out of turn and luma keying/blending them together but that obviously doesn't give the fade effect.