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 can be verified on playback using an open-source video player.[2]
I hope this sort of video signing will be mainstream in all cameras in the future (i.e. cellphones etc), as it will pretty much solve the trust issues deep fakes are causing.