This idea dates back to way before bitcoin.
> perform a mini-transaction every 30 seconds
I guess if you don't want to be blackmailed, you better have money.
Besides, techniques for identifying fakes is likely to lag closely behind the techniques for producing them.
The first time we talked about "DeepFakes", someone I know pointed out that there is nothing inherently new in this issue. Media has been faked to manipulate the truth as long as there has been media.
Wether you trust the medium, a person, or a blockchain, trust is only as good as the information you base it upon – and there's always ways to circumvent it, or otherwise deceive you.
Also: There are some pretty big privacy issues (from what I understand) with what you describe.
The courts should know that videos can be doctored, just as images can be photoshopped.
As the burden of proof lies with the accuser, it is they that would need a bullet proof argument that you did in face do what the video claims you did – and video is not alone in and of itself to establish truth.
As for the data gathering: the existence of the proposed data presents a threat for the subjects (and society) in and of itself.
Extreme surveillance, for what? To give evidence that you weren't in a fake dancing video?
I can't see this happening any time soon ...