Pluraleyes software does this using the audio recorded by each camera: https://www.maxon.net/en/red-giant/pluraleyes https://www.maxon.net/en/red-giant/plurale

Pluraleyes software does this using the audio recorded by each camera: https://www.maxon.net/en/red-giant/pluraleyes https://www.maxon.net/en/red-giant/pluraleyes If you filtered the audio to exclude all but the 50Hz/60Hz signal then it might also work based just on the power hum, but why make it's job more difficult?