I think he's refering to Character Generation. This is not something you can do within the application, but you could plug a 'CG' PC/Mac (running motion or after effects/FCP) into the video input of Catalyst and key through the black areas.

Apple have a DVI- Composite/S-Video adapter at the apple store you can buy for $20, or you can use the video desktop that Decklink and other RTE capture cards have. This is where the Decklink card outputs a video output for a monitor - depending on the card this could be composite or SDI.

We haven't tested the Decklink HDMI card yet...

H.