Instant replay is a video reproduction of something that recently occurred which was both shot and broadcast live. The video, having already been shown live, is replayed in order for viewers to see again and analyze what had just taken place. Some sports allow officiating calls to be overturned after the review of a play. Instant replay is most commonly used in sports, but is also used in other fields of live TV. While the first near-instant replay system was developed and used in Canada, the first instant replay was developed and deployed in the United States. During a 1955 Hockey Night in Canada broadcast on CBC Television, producer George Retzlaff used a "wet-film" (kinescope) replay, which aired several minutes later. Videotape was introduced in 1956 with the Ampex Quadruplex system. However, it was incapable of displaying slow motion, instant replay, or freeze-frames, and it was difficult to rewind and set index points.

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