Mirroring works fine until I try to stream video from any device

The title pretty much says it all.

I can mirror and see my Mac desktop or iPhone screen but as soon as I try to stream the video it goes black and doesn't work.

No audio or video even though I can see the time bar(?) on the Mac is ticking away seconds so the video is playing.

I've never gotten this to work and its a little frustrating.

Any help would be great. Apple TV is a little too expensive to throw out and get two fire sticks