First Appearance

The French Chef with Julia Child in 1976 on WGBH

The technology, which converts human-generated captions into electronic code that is inserted into a part of the television signal not normally seen, was refined through demonstrations and experiments funded in part by the Department of Health, Education and Welfare. In 1979, the Federal Communications Commission formed the National Captioning Institute (NCI), a nonprofit organization dedicated to promoting and providing access to closed captioning. The first closed-captioned programs were broadcast on March 16, 1980, by ABC, NBC, and PBS. CBS, which wanted to use its own captioning system called teletext, was the target of protests before agreeing to join its network brethren in using closed captioning a few years later.


Legal Stuff

In 1990, a law—the Television Decoder Circuitry Act of 1990—was passed mandating that all televisions 13 inches or larger manufactured for sale in the U.S. contain caption decoders. Sixteen years later, the FCC ruled that all broadcast and cable television programs must include captioning, with some exception (source: )

In 2014, the FCC updated their rules to require that all digital services must provide closed captioning. . (Source: )

How It Works

There are two types or formats used for closed captioning. One type involves creating a separate, distinct file that is played in conjunction with a video. The second method consists of embedding closed captioning into the video itself. When closed captioning is created in a separate file, different methods are used. These include binary, text, and XML. Closed captioning and subtitles are similar but different. While subtitles are used to translate a film into another language, they are not geared toward the hearing impaired. Closed captioning includes information beyond the dialogue of a film, like music credits, transcribed sound effects, lyrics to songs, and sometimes the name of the person speaking in a film. (Source: )

The What

The captions are hidden in the line 21 data area found in the vertical blanking interval of the television signal. If you have read the article entitled How Television Works or the question on the V-chip, then you know about the blanking interval. It is the area of the television signal that tells the electron gun to shoot back up to the upper left corner of the screen to begin painting the next frame. Line 21 is the line in the vertical blanking interval that has been assigned to captioning (as well as time and V-chip information). Each frame of video can transmit two characters of captioning information (or special commands that control color, popups, etc.) (Source:

The How


It can take up to 16 hours to caption a one-hour prerecorded program, as the process involves more than transcribing a program’s script. Using special software, the captioner must set the placement of the caption on the screen, as well as set when the caption appears and disappears. In the early days of captioning, scripts were edited for understanding and ease of reading. Today, captions generally provide verbatim accounts of what is said on the screen, as well as descriptions of sounds in the background. (Source:


Real-time captioning is typically done by court reporters or similarly trained professionals who can type accurately at speeds of up to 250 words per minute. While captioners for prerecorded programs typically use standard keyboards, a real-time captioner requires a steno machine.

A steno machine contains 22 keys and uses a code based on phonetics for every word, enabling skilled stenographers to occasionally reach typing speeds of more than 300 words per minute. Words and phrases may be captured by pressing multiple keys at the same time, and with varying force, a process known as chording. Real-time captioners, or stenocaptioners, regularly update their phonetic dictionaries, which translate their phonetic codes into words that are then encoded into the video signal to form closed captions.

The Types

Some shows are captioned in real time. That is, during a live broadcast of a special event or of a news program, captions appear just a few seconds behind the action to show what is being said. A stenographer listens to the broadcast and types the words into a special computer program that adds the captions to the television signal. The typists have to be skilled at dictation and spelling and they have to be very fast and accurate at typing.

Other shows carry captions that get added after the show is produced. Caption writers use scripts and listen to a show’s soundtrack so they can add words that explain sound effects. On a game show, for example, when there is no dialogue but there is laughter, the caption will say “Audience laughing.” (Source:

Exempt Programming

Under current federal regulations, there are two instances in which broadcasters may be exempted from closed captioning requirements. The first is self-implementing exemptions, and the FCC provides a list of all qualifying criteria. The second form of exemption is a result of economic burden to the broadcaster. Broadcast media that is subtitled may also be exempt from closed captioning requirement. (Source: )

Some Words on Terms

Closed captioning means the signal can be turned off.

Open captioning can not be turned off

Subtitles are for translations into languages different from the spoken language. They also do not include non-verbal sound. E.g *Knocking on door* or *Jaunty Music*

DIY Tools

Here are links to the list of tools Lisa mentioned if you’re interested in adding captions to your own videos:

In addition to this list, YouTube itself allows you to edit the automatically generated captions (which can be rough) or upload your own file. To access it, go to Your Profile Icon > YouTube Studio > Creator Studio Classic > Edit > Subtitles/CC


The National Center for Accessible Media at WGBH, one of the first groups to do closed captions, owns one patent. It’s for the Rear Window Caption Device. It’s a closed caption device that sits in the cup holder and allows people like me to have captions for movies.


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