closedcaption

Closed captioning is the display of text on a video screen that provides a transcription of spoken dialogue and non-speech information such as sound effects, speaker changes, and music cues. Unlike open captions, which are burned into the video and always visible, closed captions can be turned on or off by the viewer and are carried within the video signal or as a separate text track. They are primarily used to aid those who are deaf or hard of hearing, but are useful in noisy environments or for language learners.

Captioning can be automatic or produced by human captioners. Live captions are created in real time by stenographers or ASR systems, while pre-produced captions are prepared in advance. In addition to dialogue, captions may indicate non-verbal sounds (applause, bells) and speaker identifiers. Subtitles, by contrast, usually translate dialogue, while captions preserve source language and acoustics.

Standards and formats vary by region and delivery method. In the United States, traditional television used EIA-608 (line 21) with EIA-708 for digital broadcasts. Online and streaming video commonly use text-track formats such as WebVTT or TTML (DFXP), which can carry captions or subtitles. Captions may be embedded in the video stream or delivered as separate tracks that players can enable or disable.

Closed captioning has become a standard accessibility feature in many countries, supported by broadcasters, platforms, and devices. Its availability improves comprehension for non-native speakers and people with hearing loss and is increasingly integrated into educational and workplace media.