You need a capture device of some kind in between. Most computers don't have one, so you have to add it. What are you using for that?
If it's a cheap thing, then it's effectively random what you actually get, regardless of any claims. Can't really support those beyond, "get a better one." Expect to spend about $100 per channel for name brand USB, and you're still limited to one video source per USB controller, which is more restrictive than per port because most machines have internal hubs that funnel a bunch of ports back to the same controller. Or use an internal PCIe card.
Anyway, you haven't really given enough to go on, beyond that.
