Closed captioning occurs as the result of a signal concealed within the video signal that cannot be revealed without a decoder. Once decoded the captioning is unveiled and can be seen on the television screen. These signals are concealed within line 21 of what is called vertical blanking interval. Originally, it was necessary to buy a special decoder in order to take advantage of closed captioning.
The origin of closed captioning traces back to the early 1970s. In 1970 the National Bureau of Standards contracted with the American Broadcasting Company (ABC) to take part in an experiment to send precise time information via broadcast signals. The experiment failed, but ABC's recommendation that the same technology could be used to send captioning forever changed the world for millions of hearing impaired people.
Several demonstrations of closed captioning technology were held before the process moved forward toward reality. The first demonstration took place in 1971 before the First National Conference on Television for the Hearing Impaired. A second demonstration was held a year later at the country's only college for the deaf, Gallaudet University. The television show that was captioned during the Gallaudent demonstration was The Mod Squad.
The success of the demonstrations resulted in the National Association of Broadcasters agreeing that captioning was feasible, but insisting that more developments would be necessary. The federal government stepped to the plate and agreed to fund the development. The Bureau of Education for the Handicapped of the Department of Health, Education and Welfare contracted engineers working for the Public Broadcasting System (PBS) to work designing the captioning system.
During the process of fine-tuning the system of delivering close captioning, a few programs were broadcast with open captioning, or captions that appeared as part of the transmission. In 1971, Julia Child's PBS program The French Chef made history as the very first American program to deliver captions. PBS also aired a repeat of the ABC News that aired earlier, only this time with open captions, making it the very first daily news program accessible to the deaf.
In 1976 the Federal Communications Commission (FCC) officially set aside line 21 of the vertical blanking interval for the transmission of closed captions. The engineers at PBS also developed the necessary equipment to caption programs, encode them for transmissino, and then decode them at home.
Closed captioning transmission officially began in the United States on March 16, 1980. Among the programming that aired that day that were broadcast with closed captions were the Duchess of Duke Street on Masterpiece Theater, the ABC Sunday Night Movie Force 10 From Navarone, and Once Upon a Class airing as part of the The Wonderful World of Disney.