Congratulations, you have now created a class of people who can forge audio and video streams at will, relatively cheaply - and an underclass of people who cannot and may not even be able to record genuine footage they wish to record. This is not a road you want to go down.

No - I just created the equivalent to https for video; the "underclass" can still create, share and play unsigned videos - those would get low-trust warnings[1] (as they should, just like there is an "underclass" with no cert for their site). This wouldn't take away anything from todays' tech, only adds attestation for person/org behind videos they would like to mark as "official".

1. (edit) It occurred to me that some people may wish to manage the public keys independent of (say, Apple) and they could distribute via keybase or key-signing parties, so they actually don't have to suffer low-trust warnings. Now that I think of it, instead of merely signing streams, they could be signed and encrypted using recipients PK for 1:1 transmissions. Obviously law enforcement won't be a fan

Law enforcement will just coerce the CA system you've suggested to secretly improperly issue certificates. Just as it does with the current CA system. Problem not solved - it's just hidden.

You conflate content trustworthyness with origin sureity but a CA system doesn't even provide that.