Have a vague memory of some old HN discussion about how known fluctuations in light because of slightly varying electricity frequency have been used already to detect fake video and that databases exist with information about frequencies by location and time for this purpose?
https://pmc.ncbi.nlm.nih.gov/articles/PMC9304164/
> Electric network frequency is a signal unique over time and thus can be used in time estimation for videos.
Might have been audio?
https://phys.org/news/2018-02-power-grid-fluctuations-hidden...
Sibling comment and article mentioning "Electric network frequency (ENF)" lead to further reading mentioning both audio and visual fluctuations being used.
Ah you’re right. Pretty cool.