Unique digital codes are encoded on a video signal, the codes are retrieved at receivers and precise information concerning the time of occurrence, length, nature and quality of a monitored broadcast at a frame by frame level, is generated. The codes are inserted on scan lines of the video, and vary...http://www.google.com.au/patents/US5646675?utm_source=gb-gplus-sharePatent US5646675 - System and method for monitoring video program material
