Closed captioning
Closed captioning allows deaf, hearing-impaired, and other people to see, through captions, the audio portion of a video that they cannot hear. As the video plays, captions showing what is being said and by who, as well as other miscellaneous sounds, is displayed along with the video. The captions are closed because they are optional: hearing viewers need not see them.
Captions are distinct from subtitles: subtitles assume the viewer can hear but cannot speak the language, so they only note dialogue. Captions describe all the audio content, as well as information about the identity of speakers and their tone of voice.
Television
Spoken words comprising the television program's soundtrack are transcribed by a court reporter (in the case of live programs), done using stenotype or stenomask techniques, or are separately prepared in advance and encoded into line 21 of the television signal, which is the last line of the vertical blanking interval. Sometimes music or sound effects are also described using words or symbols within the closed caption. (The above refers to the NTSC television format used in Canada, the US, Japan, and a few other countries. Captioning is transmitted and stored differently in PAL and SECAM countries, but the methods of preparation are similar.)
Under normal conditions, the vertical blanking interval containing the captioning information is invisible to television viewers (this is why it's called closed-captioning). However, a person may activate the closed-captioning feature found on most modern television receivers, thereby causing the program's spoken-word dialogue to be displayed onscreen. Certain video presentations (now very rare) actually have the captions permanently burned into the video instead of encoded in the vertical blanking interval; this is known as open-captioning.
Since 1993, when the Television Decoder Circuitry Act became U.S. law, manufacturers of most television receivers sold in the U.S. have been required to include closed captioning. High-definition TV sets, receivers, and tuner cards are also covered, though the technical specifications are different.
There are three methods of captioning:
- Roll-Up: The words appear from the left corner, one at a time, and when a line is filled the whole line scrolls up to make way for a new line, and the line on top is erased. The captions usually appear at the bottom of the screen. This method is used for live events, where a sequential word-by-word captioning process is needed.
- Pop-Up: The caption would appear anywhere on the screen as a whole. The caption that preceded would be removed from the screen. This method is used for most pre-taped television and film programming.
- Paint-On: The caption, whether it be a single word or a line, would appear on the screen but unlike pop-up, the previous caption may not be removed from the screen before the new caption is ‘painted on’ to the screen.
Electronic caption text inludes the symbols '>>' to indicate a new speaker, and '>>>' in news reports to identify a new story. Capitals are used because there is reported to be no descenders for lowercase i, j, g, q, and y (i.e. they would be hard to read because they would be put on a line used by other letters). Text can be italicized; in fact the FCC standard requires that text meant to be in italics be rendered that way on television displays.
Movies
Movies can be captioned using the Rear Window Captioning system. A reflective plate is placed on a stick in front of your seat. The plate reflects an electronic display at the back of the theater, which shows the movie's captions in reverse. When the system is working properly, the reflective plate makes the captions appear properly below the film.
Telephones
Closed captioning is now starting to be applied to telephones for the hard-of-hearing and deaf. For more information, see Captioned Telephone (CapTel).