Subtitles or closed captioning are textual versions of the dialogue, usually displayed at the bottom of the screen with added information, such as speaker IDs and sound effect descriptors, to aid the deaf or hard-of-hearing viewers in following the dialogue. Users of closed captioning and subtitles include people who have experienced hearing loss later in life and those who have been deaf since birth. In addition, some people use these captioning services for other reasons, such as to watch television with the sound muted or to learn English, though they are not the target audience.
For the visually impaired, it is difficult to follow the action on the screen when there is little dialogue. Audio description provides narration describing the action taking place on-screen to help viewers with visual impairments to follow the plot. This audio description is recorded and made available as a separate audio track that can be selected by the viewer.