It's never exactly 50 Hz, as the frequency is affected by load and generators can't compensate this perfectly. So record it in many locations, then correlate th

It's never exactly 50 Hz, as the frequency is affected by load and generators can't compensate this perfectly. So record it in many locations, then correlate the signal extracted from audio/video against the database. Main article: https://en.wikipedia.org/wiki/Electrical_network_frequency_analysis https://en.wikipedia.org/wiki/Electrical_network_frequency_a...