I work at Axis, which makes surveillance cameras.[0] This comment is my own, and is not on behalf of the company. I'm using a throwaway account because I'd rather not be identified (and because surveillance is quite controversial here). Axis has developed a way to cryptographically sign video, using TPMs (Trusted Platform Module) built into the cameras and embedding the signature into the h.264 stream.[1] The video c…
That will just move the hack one level further down and will create even more confusion because then you'll have a 'properly signed video stream' as a kind of certificate that the video wasn't manipulated. But you don't really know that, because the sensor input itself could be computer generated and I can think off the bat of at least two ways in which I could do just that.
So, the best you get is that the stream shows it wasn't produced with access to a particular camera. Then impersonating a YouTuber, say, requires access to their physical camera.