Product description "Video Headroom Systems - Scanners"
The concept of Scanners is simple but very creative and can be used in many ways. You have three inputs for video signals, between which you can scan, morph, or fade (different terms for the same effect) manually or with control voltages, and you can do this twice.
Finally, there is an output for each of the channels, but also a sum output, which is the combined output of both channels.