That will get tricky as the second you upload a video to youtube or any cloud service, it gets transcoded into dozens of other different sized and formatted videos, which will effectively strip all that out. But I'm sure we could still come up with some solution that uniquely identify the source somehow.
Reality Is Melting as Lawyers Claim Real Videos Are Deepfakes (futurism.com)
Generative AI-powered tools are making it easy to create deepfakes — and lawyers are trying to seize the moment as an opportunity.