I don't believe much can be done with amateur videos, but official videos of celebrities could be cryptographically signed with a key only known by that celebri

I don't believe much can be done with amateur videos, but official videos of celebrities could be cryptographically signed with a key only known by that celebrity/their PR manager. That of course could lead to celebrities not signing unfavorable videos. Also the average info consumer wouldn't bother downloading and confirming the signature.