How to add a button overlay to video camera screen? - with example

I want to create an overlay on top of a streaming video screen. An actionable icon. Video example attached bu here’s what I’m looking to do:

Watch this video and you’ll see why. I also want to use it to open my front gate while watching the cam - click on the icon to open my gate.

Any ideas?? Im open to all suggestions and have lots of plugins, one of which might work here.

Jeff