Captions are a transcription of all audio elements of a video, including dialogue, sound effects, and descriptions of music and song lyrics if they are important in the context of the video. Captions generally appear at the bottom of the screen and are synchronised with the video’s audio track. They are now becoming more common on online videos, with most media players supporting them.
Captions may be either ‘open’ or ‘closed’. Open captions are encoded onto a video (i.e. they are part of the video image itself) and will be seen by anyone who watches it. Closed captions can be turned on and off by the viewer.
To comply with WCAG 2.0 Level A, captions must be provided for all pre-recorded audio-video content (Guideline 1.2.2). For those who want to meet WCAG 2.0 AA, all live audio-video content must also have captions (Guideline 1.2.4). At WCAG 2.0 AAA, caption is required for live audio-only content (Guideline 1.2.9).
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