Chroma Key Live is a free tool to generate a live "green screen" composite (AKA "chroma key") during a video shoot.
In the days of analog video, the camera's live signal was routed through a keyer in the control room and delivered back to an on-set monitor. This way, the production team could see exactly how the actor looked when composited over the background image. Modern digital video is shot without the support of an analog studio, so the chroma key is created afterwards inside the computer. This leads to a problem: How do you visualize the composited image on-set when all you can see is the actor against a green screen?
Now it's simple: Run the Firewire output from your camera into a laptop running Chroma Key Live. Click on the live video image to choose your key color and load a Quicktime background file (movie or still image). Now you can see your actor composited on top of your background!
(Note: Chroma Key Live cannot record. It is strictly for on-set preview. You can do much better keys in post-production software.)
Note: While the software is classified as free, it is actually donationware. Please consider making a donation to help support development.