How it works

What is closed captioning?

Like subtitles on movies, captions are transcriptions of the spoken word into a written form that permit deaf and hard of hearing people to see what they cannot hear. Unlike subtitles, captions also provide descriptions of sounds, such as a bell ringing or a door slamming. There are two kinds of captioning-open and closed. Open captions always appear on the screen, while closed captions are carried in the television signal in hidden form and must be “opened” (electronically decoded) to be seen. Closed captioning is the process whereby captions are converted to electronic codes and inserted in the regular television signal, specifically on Line 21, a portion of the picture normally not seen. There are 525 horizontal lines in the television picture. Line 21 appears at the top of the picture and occurs just prior to the start of the lines carrying picture information.

How are closed captions accessed?

Closed captions are hidden within normal television broadcasts and on videotapes and DVD’s. All you need is a television with the built-in caption decoder chip or an external decoder to make the captions visible. There’s no special service to subscribe to in order to receive the captions. Rather, captioning is made free for all viewers by the television and home video industries and with the support of grants and donations.

Just look for NCI’s registered trademarks, which mean a program or video has been captioned by the National Captioning Institute. Or you can look for the generic (CC) symbol that also indicates a program is captioned.

What do captions look like?

Captions are easily visible white letters against a black background, strategically placed on the television screen so that they do not obstruct relevant parts of the picture. Caption size varies proportionally with the size of the television screen. On a 19-inch screen, for instance, captions are 0.5″ inches high. NCI provides English captions in all upper-case letters to improve readability on smaller television screens and in situations when picture clarity is impaired. Spanish captions are provided in mixed case to enable the use of accent marks.