@icedquinn you break the video up into chunks and sign the chunks.

this obviously doesn't work with edited video but if one were serious, you could add a metadata stream that links timestamps with a signature fingerprint so that a human could do a visual inspection to see if a video plausibly is the same after resampling.

there's no infrastructure for this at all and I don't believe for a second that the white house is going to start making all their videos cryptographically signed and the raw video available on bittorrent or something. it's just not going to happen. it would be cool if it did.