Can you tell us a bit more about what you’re trying to do? You can definitively use the Xibo player as a source for on screen text and graphics, but you’d need another system to overlay video in an area on screen or knock out using chromakey. What you’re probably better off doing is using a character generator platform like Caspar CG to add content over live video.
That being said, there is a live video module in Xibo, see Streaming live video to Xibo .NET client for some more info.
-DJ