Import the green screen footage into After Effects and key it out using Keylight.
Then, you have two choices. You can use Dynamic Link to link the comp back into Premiere Pro. That is great when you are in a hurry and are still making changes, but it can be tough on the PC.
Once I have it where I am really sure I want it, I often export from AE into Quicktime using the Animation codec with Alpha channel. Then I replace the Dynamic Link with the exported footage.
I have also been known to do the keying and then superimpose it over the footage I plan to use. Then I can export from AE using Cineform HD AVI and when I bring it back to Premiere Pro there is no rendering required.
I avoid exporting until the system bogs down. If it never bogs down then keep using the Dynamic Link.
Steven
http://www.stevengotz.com
