That’s true, but the more transparent and obvious the evidence against misinformation, the more people will disregard it. You’ll always get the gullible minority that’ll believe in whatever conspiracy, but democracy doesn’t hinge on them, it hinges on the quiet majority.
That said, this should be done in a privacy respecting way. You should be able to choose not to have your videos signed, not to associate that signature with a given account, and to supply your own signing key. Device resets should reset the key as well. There should also be a mechanism to associate multiple devices as coming from the same source, while distinguishing between devices (so if one device is compromised, only those videos are suspect).
I think it could be done pretty unobtrusively, and it should start as a standard for journalism before going to the broader public.