The devices need to cryptographically sign the original video with keys stored in some kind of Secure Enclave

If the video is edited or comes from a source that doesn’t have trusted keys then it’s no better than some random tweet

This is just a certificate of authenticity that one either trusts or not, based on whatever one knows about secure enclaves, cryptography, or the device/person issuing the key/certificate.

I think the reality is that photographs and video are now like text, you trust the source or not.

I can write about Cleopatra's ability to snowboard and play Xbox, or I can make a photo with the caption "Cleopatra doing a 1080", and now I can make a video of it (probably).

I can also give you a certificate/key/blockchain whatever to prove it's "valid".

And then someone takes the camera and points it at a screen showing an image of their choice. The analog hole cuts both ways.