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Television and video

For live programs, spoken words comprising the television program's soundtrack are transcribed by an operator using stenotype or stenomask type of machines, whose phonetic output is instantly translated into text by a computer and displayed on the screen. This technique was developed in the 1970s as an initiative of the BBC's Ceefax teletext service.[1] In collaboration with the BBC, a university student took on the research project of writing the first phonetics-to-text conversion program for this purpose. [2] (PDF) Automatic computer speech recognition now works well when trained to recognise a single voice, and so since 2003 the BBC does live subtitling by having someone re-speak what is being broadcast.

In some cases the transcript is available beforehand and captions are simply displayed during the program after being edited. For programs that have a mix of pre-prepared and live content, such as news bulletins, a combination of the above techniques is used.

For prerecorded programs and home videos, audio is transcribed and captions are prepared, positioned, and timed in advance.

For all types of NTSC programming, captions are "encoded" into Line 21 of the vertical blanking interval – a part of the TV picture that sits just above the visible portion and is usually unseen. For ATSC (digital television) programming, three streams are encoded in the video: two are backward compatible Line 21 captions, and the third is a set of up to 63 additional caption streams encoded in EIA-708 format.

Captioning is transmitted and stored differently in PAL and SECAM countries, where teletext is used rather than Line 21, but the methods of preparation are similar. Note that, for home videotapes, a variation of the Line 21 system is used in PAL countries. Teletext captions can't be stored on a standard VHS tape (due to limited bandwidth), although they are available on S-VHS tapes.

For older televisions, a set-top box or other decoder is usually required. In the U.S., since the passage of the Television Decoder Circuitry Act, manufacturers of most television receivers sold have been required to include closed captioning. High-definition TV sets, receivers, and tuner cards are also covered, though the technical specifications are different. Canada has no similar law, but receives the same sets as the U.S. in most cases.

There are three styles of Line 21 closed captioning:

• Roll-up or scroll-up or scrolling: The words appear from left to right, up to one line at a time; 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, but can actually be placed anywhere to avoid covering graphics or action. This method is used for live events, where a sequential word-by-word captioning process is needed.

• Pop-on or pop-up or block: A caption appears anywhere on the screen as a whole, followed by another caption or no captions. 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, appears on the screen letter-by-letter from left to right, but ends up as a stationary block like pop-on captions. Rarely used; most often seen in very first captions when little time is available to read the caption or in "overlay" captions added to an existing caption.

A single program may include scroll-up and pop-on captions (e.g., scroll-up for narration and pop-on for song lyrics). A musical note symbol is used to indicate song lyrics or background music. Generally, lyrics are preceded and followed by music notes, while song titles are bracketed like a sound effect. Standards vary from country to country and company to company.

For live programs, some soap operas, and other shows captioned using scroll-up, Line 21 caption text includes the symbols '>>' to indicate a new speaker (the name of the new speaker sometimes appears as well), and '>>>' in news reports to identify a new story.In some cases, '>>' means one person is talking and '>>>' means two or more people are talking. Capitals are frequently used because many older home caption decoder fonts had no descenders for the lowercase letters g, j, p, q, and y, though virtually all modern TVs have caption character sets with descenders. Text can be italicized, among a few other style choices. Captions can be presented in different colors as well. Coloration is rarely used in North America, but can sometimes be seen on music videos on MTV or VH-1, and in the captioning's production credits. More often, coloration is used in the United Kingdom and Australia for speaker differentiation.

There were many shortcomings in the original Line 21 specification from a typographic standpoint, since, for example, it lacked many of the characters required for captioning in languages other than English. Since that time, the core Line 21 character set has been expanded to include quite a few more characters, handling most requirements for languages common in North and South America such as French, Spanish, and Portuguese, though those extended characters are not required in all decoders and are thus unreliable in everyday use. The problem has been almost eliminated with the EIA-708 standard for digital television, which boasts a far more comprehensive character set.

Captions are often edited to make them easier to read and to reduce the amount of text displayed onscreen. This editing can be very minor, with only a few occasional unimportant missed lines, to severe where virtually every line spoken by the actors is condensed. The measure used to guide this editing is words per minute, commonly varying from 180 to 300, depending on the type of program. Offensive words are also captioned, but if the program is censored for TV broadcast, the broadcaster might not have arranged for the captioning to be edited or censored also. A television set top box is available to parents who wish to censor offensive language of programs, the video signal is fed into the box and if it detects an offensive word in the captioning, the audio signal is bleeped or muted for that period of time.

There are some instances when the audio track of a TV program is altered -- useless dialog is silenced, words are bleeped, a licensed song in a syndicated TV episode is removed, etc. -- however, the captions of the removed dialog or lyrics remain. This can have serious consequences, as when a person's name is bleeped in the audio track for legal reasons but is included in the captions.