green screen monitor with moving actor behind it.

An OTS shot with green screened monitor and the actor gets up and leave the space crossing the screen. How to insert animation on the green screen and track his movement across the green screen? Camera is on tripod with no movement or panning.

So there is no actual movement to track? Only that of the actor?
If the greenscreen is good enough, you can just key they actor out. I am not sure if I understand what the problem is.

I'm wondering if you have a full understanding of how to use the green screen aspect.

The point of the green screen should be to insert your animation into it (key it into the monitor) and any fg or bg elements will be separated from the monitor automatically.

Unless your actor is wearing green?

If for some reason your actor is keying out as well, either your key needs to be adjusted, i guess you will have to roto him/her as they cross the monitor.

Draw a polygon shape around them, and animate it as they cross the monitor.

Didn't understand either...