[elephant0xffff]

> Some sort of service that signs and proves the authenticity of videos.

I don't think that is even possible.

You might want to succeed with amateur efforts, but I would guess there will be a point where it is impossible to tell if a video is fake or not.

[gonehome]

Just sign it after you verify the original person’s identity so you know if it’s been tampered with.

Company would be responsible for effectively verifying identity - similar to how this is done for websites.