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Re:Samsung remotely disables TVs looted from South African w... by crysin on Tuesday August 24, 2021 @02:35PM (#28293008)
https://en.m.wikipedia.org/wiki/Cinavia

Slightly different than what gp was talking about but also deals with using invisible audio for DRM

Re:Samsung remotely disables TVs looted from South African w... by benttoothpaste on Tuesday August 24, 2021 @04:29PM (#28294581)
Audio is usually invisible