Creating a virtual green screen with Arnold shaders

Though render layers are more commonly used for these instances, this was an idea I thought would work as I wanted to be able to retain its original reflection of the characters within the tv up close.

Two scenes in my animation have a televisions scene where the camera zooms in and transitions to a new shot which is depicted within it. Earlier in the development I did this test using an Arnold shader using green a screen color range and a still camera, it worked quite well. Upon editing the final television things quickly became problematic when I realized I made a few minor errors. I had a few other green colors in the scene so after applying Chroma Keyer in Sony Vegas it essentially applied the filter across all green elements within the image. To fix this I figured out that you could animate a mask to the area of the screen, as the camera moves and pans in both scenes meant making adding a number of keys across the whole sequence.