John G Lert Jr, Daozheng Lu: Broadcast program identification method and apparatus. A C Nielsen Company, Mason Kolehmainen Rathburn & Wyss, June 30, 1987: US04677466 (646 worldwide citation)

A method and apparatus for identifying repetitively broadcast programs, such as commercial advertisements broadcast on television and radio, detects the occurrence of predetermined events in a video signal and/or in an audio signal, detects a stability condition and extracts a signature from the vid ...