If you haven't known, closed captioning is a process of displaying text on a television or video screen for hearing impaired viewers. Other nicknames for closed captioning are Line 21 or EIA-608. Closed captioning was mainly used in North America, while in later years, several other countries that also support NTSC have carried it as well.

A few years after the Television Decoder Circuitry Act of 1990 became law early in 1991, all television sets measured at 13 inches or longer manufactured since that time were given built-in closed captioning decoders. These TV sets offered two channels for closed captioning (CC1 and CC2), while later sets also carried an additional two channels (CC3 and CC4).

Originally, the Closed Caption Character Set comprised of 112 different characters (96 Standard and 16 Special). Standard Characters included all 26 letters of the Latin alphabet (both uppercase and lowercase), the numbers 0-9, each of the lowercase Latin vowels with an acute, lowercase C with a Cedilla (ç), and both uppercase and lowercase N with a Tilde (ñ). Special Characters included the upside down question mark (¿), the pound sign for British currency (£), and the very commonly used musical eighth note.

In 2001, a new set of Extended Characters was introduced. Comprising of 64 characters, most older television sets and software do not support this set, and may therefore require substitute Standard or Special Characters in order to be displayed properly. Extended Characters include uppercased vowels with acutes (such as É and È) and the right single quotation mark (), which is often used as an apostrophe. Regularly scheduled closed captioning with support for Extended Characters began in 2004, usually only covering newer episodes, programs and movies on television and home media. However, not all Extended Characters were in use. For example, the Media Access Group at WGBH uses uppercase vowels with acutes and Cs with cedillas, but not quotation marks.

On February 9, 2003, the Scenarist Closed Caption Tools package was introduced for those who were interested in making their own closed captions on their PCs. Each closed captioning file can be stored in the .SCC format.

How it works

  • Under normal circumstances, a speaker is identified through the placement of his/her caption. In such cases, an ID may be added to the beginning of the caption if the dialogue comes from a character that is either offscreen, or within a background appearance where he/she is not the focus. This also applies to sound effects.



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