splitting then fusing frames
 

I'm trying to make a track motion color that I can turn transparent and block everything but the actor out of a shot. Anyone know a good way?

Re: splitting then fusing frames
 

Chroma key is the easiest way to do this.
If that's not an option, then try a technique called difference compositing.
Here's a tutorial on it.

Two cats from one

Re: splitting then fusing frames
 

I may be looking for a moving matt since the cam is locked down and the background remains the same.

Re: splitting then fusing frames
 

Both options I suggested would need to be done at the time of shooting so you'll need a motion tracker to do this in post. I believe that Boris FX has one that works with Vegas.