With video signals, IO is costly because they all have to run synchronous to each other in order to mix and interact in the analog domain. With Cortex, you get one input for “free” because Cortex can slave its own timing to the timing of that first external device. To get more inputs in, you need a TBC/frame synchronizer module. We have our new design for that, which is a dual input and due out this year:
https://www.lzxindustries.net//shop/product/lzxotbc2-tbc2-3019
You could also use a second Cortex to get a second input in, but the second external device would need to have a genlock feature itself. Here’s a good thread on that:
If you poke around the forums or type “sync” into the search bar, you’ll find more info on video synchronization topics. Let me know if you have more questions!