My plan to solve this "20 second bit of it" is that it's done at the analog hole. Whatever is painting those pixels, a smart TV for instance, will be coordinating with cloud services to fingerprint at a relatively high temporal resolution - maybe 5 seconds. The video itself is the signature. But we will need either trusted analog hole vendors or some trusted non-profit organization - or likely both. I think that "viewing" will be delayed by perhaps 30 seconds to allow for that signature analysis. These smart TVs will overlay a scorecard for all displayed content, and owners will be able to set device scorecard thresholds such that low-scoring content will be fuzzed out.