As I was preparing the requirements for an accessible web video player, there was some confusion around subtitles, closed captions, audio descriptions and transcripts. In this post, I use interactive examples to show the difference. I also provide related success criteria from the Web Content Accessibility Guidelines (WCAG).
Subtitles
Subtitles are text tracks matching only spoken dialogs of an audio track. They're meant for people who perceive the audio but need the text for clarification or language translation, e.g., when watching a movie in a foreign language.
Subtitles are neither required nor sufficient to fulfil WCAG.
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Hello?Closed captions
Closed captions (CC) are text tracks transcribing the information within an audio track, including dialogs, music and sound effects. They're necessary for viewers who can't perceive the audio to understand what's happening, e.g., deaf or hard of hearing people.
Closed captions are required for videos to fulfil WCAG Level A (SC 1.2.2).
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Suspenseful music playing. Door creaking.
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Female voice: Hello?Audio descriptions
Audio descriptions are audio tracks describing visual elements of the video content, including setting, costumes, gestured or facial expressions. They help viewers who can't perceive the video to understand what's occurring on screen, e.g., blind or low-vision people.
Audio descriptions are required for videos to fulfil WCAG Level AA (SC 1.2.5).
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An old door opens.
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A decayed room in an abandoned building.
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Sunlight shines through a window.Transcripts
Transcripts (transcriptions) are text versions of the audio and video content. Descriptive transcripts are needed by people who are deaf-blind and others.
Transcripts are required for videos to fulfil WCAG Level AAA SC 1.2.8.
Suspenseful music is playing.
An old door creaks while it opens.
A decayed room in an abandoned building appears.
Sunlight shines through a window.
Female voice: Hello?Summary
- Subtitles describe dialogs via text.
- Closed captions describe the audio track via text.
- Audio descriptions describe the video track via audio.
- Transcripts describe the video and the audio tracks via text.
For pre-recorded videos containing an audio track, closed captions and audio descriptions are required to fulfil WCAG Level AA.