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Using the track element to provide captions
From WCAG WG
- New technique.
This technique would be listed as one of the technology-specific techniques implementing G87, listed in the third bullet of sufficient techniques in Understanding 1.2.2.
- media-equiv-captions: SC 1.2.2 Captions(Prerecorded) (sufficient)
User Agent and Assistive Technology Support Notes
In addition to evaluating the support for the track element in user agents, do we also need to assess the conformance of the player used to activate captions? If custom controls are needed to provide access, do we need to create a technique for the controls and include them as part of the sufficient technique?
The objective of this technique is to use the HTML5
track element to specify a
caption timed text track for a
video element. Caption timed text tracks contain transcription or translation of the dialogue, sound effects, relevant musical cues, and other relevant audio information, suitable for when sound is unavailable or not clearly audible.
src attribute of the
track element is a URL that is the address of the text track data.
kind attribute of the
track element indicates the kind of information in the timed text.
caption text tracks provide the dialogue and also include other sounds important to understanding the video.
subtitles contain only the dialogue. If other audio information is important to understanding the video, a subtitle track will not be sufficient to meet the success criteria.
Note: Some cultures use the term "subtitle" for any visible text representation of the audio track. An author may mark up a timed text track in the language of the audio track as
kind=subtitle, instead of
kind=caption, and may include additional relevant audio information. It is not best practice to use
subtitle in this situation, since it may confuse users who are trying to find captions. But such a timed text track would meet the requirements of Success Criterion 1.2.2.
A video element for a video in the English language with an English caption track. srt is a common caption format.
<video poster="myvideo.png" controls> <source src="myvideo.mp4" srclang="en" type="video/mp4"> <track src="myvideo_en.srt" kind="caption" srclang="en" label="English"> </video>
A video element for a video with both an English and French language source element, and with an English caption track and a French captions track. WebVTT (wtt) and Timed Text Markup Language (ttml) are different caption file formats.
<video poster="myvideo.png" controls> <source src="myvideo.mp4" srclang="en" type="video/mp4"> <source src="myvideo.webm" srclang="fr" type="video/webm"> <track src="myvideo_en.wtt" kind="caption" srclang="en" label="English"> <track src="myvideo_fr.ttml" kind="caption" srclang="fr" label="French"> </video>
video element used to play a video:
- Check that the video contains a
trackelement of kind
captionin the language of the video.
- Check that #1 is true