Earlier quoted context omitted.
I suspect we're headed into a world of attestation via cryptographically signed videos. If you're the sole witness, then you can reduce the trust in the event, however, if it's a major event, then we can fall back on existing news-gathering machinery to validate and counter your false tagging (e.g. if a BBC camera captured the event, or there is some other corroboration & fact checking).
How does the signature help? It only proves that the video hasn't been altered since [timestamp]. It doesn't prove that it wasn't AI-generated or manipulated.
Everything else - corroboration, interviews, fact checking will remain as they are today and can't be replaced by technology. So I imagine a journalist would reach out to person who recorded thr video, ask them to show their device's fingerprint and ask about their experience when (event) occured, and then corroborate all that information from other sources.
When the news org publishes the video, they may sign it with their own key and/or vouch for the original one so viewers of clips on social media will know that Fox News (TM) is putting their name and reputation behind the video, and it hasn't been altered from the version Fox News chose to share, even though the "ModernMilitiaMan97" account that reshared it seems dubious.
Currently, there's no way to detect alterations or fabrications of both the "citizen-journalist" footage and post-broadcast footage.