On television, captions can be turned on using the setup command and selecting CC (or CC1, CC2). With a television, the captions are added to a video using” line 21″ of the vertical blanking interval in the analog video signal. Government regulations specify the encoding method, available characters and caption layout (32 characters in four of 15 lines).
To see the captions, a decoder is needed in the television set. Decoders are now built into all televisions sets made in the US which are greater than 13″ diagonal. These decoders interpret the information on line 21 and display the captions on the viewer’s screen.
To obtain captions for broadcast media, please see our broadcast captions page.
Real-time captions are typed by a person listening to the broadcast material in real time, either in person or via a phone line. A broadcast system will often enable the viewing of real-time captions over the Web or with a local display. Because real-time captioning requires the stenographer or typist type as fast as the speaker, error rates are high and segments are sometimes omitted due to the inability of the stenographer to keep up. AST does not provide any real-time captions.
Offline captioning refers to captioning that is done after the event, usually using a recorded audio track. Offline captioning accuracy rates are generally much higher than real-time. Offline captioning allows the stenographer to look up words, check names and spelling, and to edit content before publishing. A trained stenographer might take anywhere from 5-10 hours to transcribe an hour of audio, with a goal of greater than 99% accuracy.
Closed captioning simply refers to the ability of the viewer to turn captions on or off. Open captioning refers to captions that are superimposed on the screen and cannot be turned off.
The term subtitle is similar to captions. Both captions and subtitles are words that are synchronized with audio and video and displayed in a screen. Most popular uses of subtitles have been with foreign films, where the audio and video are synchronized but the captions are native language-specific. But when the subtitle is the same as the language as the audio and all non-dialog audio such as [ Laugh ] or [ Phone Rings ] is present, subtitles are functionally equivalent to captions (this is called SDH). In the web realm, captions and subtitles are similar terms.
Frequently, media that teaches language skills will highlight specific words for emphasis. Research shows that hearing and reading the word result in improved comprehension and retention. Highlighting of words can be done in a moving ‘Karaoke’ format, or as highlighting in a rolling line. Word highlighting can be combined with same language subtitles or second language subtitles, where the audio and subtitles are in different languages.
Closed captions refer to the user’s ability to open and close captions through the use of a button or symbol. Some browsers require you to configure a setting to enable viewing of the captions. Closed captions are usually displayed as white block letters on a black background. The video player interprets markers that contain timecodes from the caption files CaptionSync provides. This identifies the exact positions where each subtitle should appear and disappear. The end result is a subtitle file containing actual subtitles and position markers.
Each of the media players handles closed captions slightly differently. Often the captions files are a separate file which is stored in the same directory as the media assets. With some players, such as Windows Media, the player will recognize the file if it is present and make the captions available. See our How-To Tutorials for completing your captioning work with the player type you’ve chosen.
Flash offers developers several options for displaying captions. Several “skins” or Flash players, are available with Flash or via download from Adobe’s accessibility page to allow Flash developers to quickly implement captions with Flash video. Alternatively, there are prebuilt Flash video players such as the JW FLV Player and Flowplayer which support captions.