You could but then that only really works for rehosting the exact same video. Most places would at least embed it in another video for commentary which would have a reencoding step that would wipe out the original video. See my other comments for more detail but it would require changing how we handle videos to preserve the signing info.

That's a problem with embedding then, not with compression, right? Would embedding a raw video with commentary not also have the same problem?

Follow the discussion chain back up: jacobsimon's posed the question: "How would that work with video editing?"

The answer is that it doesn't. Some might try to make it work by using proprietary video editing software that signs a ledger of what edit operations were performed, or something like that, but that doesn't work. The signing keys will eventually be extracted from the video editor or the camera, or the video editor or camera will be hacked to sign something it shouldn't. You might say that this at least stops low-skilled attackers, but the misinformation that is most dangerous to humanity, that created by governments to start wars, won't be impeded by any of these schemes. The whole cryptographic signature proposal is worse than useless.

You've nailed it this whole thread is about actually using the footage in anything other than it's raw original format. As soon as you start embedding it in other footage to say present and comment on it you run into all sorts of issues dealing with maintaining the signatures.