Our company wants to be able to have LCD TVs displaying TV with the ability to add an overlay, like a stock ticker at the bottom of the screen, where human resources can add content to be displayed.

I have been trying to nail down the correct terminology for this and come across terms like Keying, Compositing, Live Broadcast Graphics Presentation, and Hardware Overlay but I don't know which of these terms is truly the correct way to refer to what I am trying to do.

Black Magic offers a product that seems like it can do what I am looking for but their product seems like it is geared for a totally different purpose than what I would be using it for.

Compix also seems to have a product that would do what I need but again it seems like killing a fly with a sledge hammer.

How can I to take an HDMI TV broadcast and overlay arbitrary content in real time?