How on top of security do you think all the camera manufacturers are going to be? That is, how long until people can sign videos that were not, in fact, shot with their camera?

Proving that you were able to upload something that is not real would go viral so it's very attractive to people to share such findings, meaning it would not last long, then they fix it and that's it, specially because they can require you to upgrade your camera's firmware if you want to keep using their attestation service.