Closed captions are captions that
are hidden in the video signal, invisible without a special decoder. The
place they are hidden is called line 21 of the vertical blanking interval
(VBI). A law in the United States called the Television Decoder Circuitry
Act of 1990 mandates since July 1993, that all televisions manufactured
for sale in the U.S. must contain a built-in caption decoder if the picture
tube is 13" or larger.
In 1970 the National Bureau of Standards
(NBS) began to research the possibility of using a portion of the network
television signal to send precise time information on a nationwide basis.
The ABC-TV network agreed to be involved in the research and development.
The project didn't pan out, but ABC suggested that it might be possible
to send captions instead.
Captioning was first previewed to
the public in 1971, at the First National Conference on Television for
the Hearing Impaired in Nashville, Tennessee. A second preview of closed
captioning was held at Gallaudet College on February 15, 1972. ABC and
the NBS presented closed captions embedded within the normal broadcast
of the television show The Mod Squad. The federal government funded
the final development and testing of this system. The engineering department
of the Public Broadcasting System started to work on the project in 1973,
under contract to the Bureau of Education for the Handicapped of the Department
of Health, Education and Welfare (HEW).
The Federal Communications Commission
set aside line 21 in 1976, for the transmission of closed captions in the
United States. PBS engineers then developed the caption editing consoles
that would be used to caption prerecorded programs, the encoding equipment
that broadcasters and others would use to add captions to their programs
and also prototype decoders.
On March 16, 1980, the first, closed
captioned television series was broadcast. The captions were seen in households
that had the first generation of the closed caption decoder. The ABC Sunday
Night Movie (ABC), The Wonderful World of Disney (NBC), Masterpiece Theatre
(PBS) were all broadcast on March 16, 1980.
In 1982, the NCI developed real-time
captioning, a process for captioning newscasts, sports events or other
live broadcasts as the events are being televised.
on Closed Captioning
Captioning Web - How To Become a Captioner
Brief History of Captioned Television
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