You can always retroactively sign. Or it would require secretive hardware managed by some centralized authority, and would be exploitable by at least nation state actors.
Signing it doesn’t mean “not modified”, it means “yes, this video is from that person”, basically, nothing more. However, that signature is something that can’t be faked.
At least with that you can state that a video came from a journalist themselves. If that’s enough to trust it, is another question
You can always retroactively sign. Or it would require secretive hardware managed by some centralized authority, and would be exploitable by at least nation state actors.
Signing it doesn’t mean “not modified”, it means “yes, this video is from that person”, basically, nothing more. However, that signature is something that can’t be faked.
At least with that you can state that a video came from a journalist themselves. If that’s enough to trust it, is another question