Using the track element to provide captions

Status

• 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.

• HTML Techniques Task Force for March 19

• Added to XML as H95

Applicability

• HTML5

This technique relates to:

• media-equiv-captions: SC 1.2.2 Captions(Prerecorded) (sufficient)

User Agent and Assistive Technology Support Notes

• March 2012: Internet Explorer 10 Platform Preview 4 includes TTML and WebVTT track caption support.
• Per discussion at the Foundations of Open Media Standards and Software developer workshop in November 2013, WebVTT captions as HTML5 video tracks are supported in all major browsers (Webkit/Safari, Blink/Chrome/Opera, Internet Explorer, Firefox (not yet released, but in nightly build), Android).
• As of November 2013, TTML captions as HTML5 video tracks are support in Internet Explorer.
• Captionator is a JavaScript polyfill designed to provide support for the <track> element. As of Jan 2014, it supports subtitles in SUB, SRT, Youtube's SBV, WebVTT, and WebVTT with Google's proposed timestamp syntax. It plans support for LRC, DFXP/TTML and the WebVTT v2 proposed features.

Description

The objective of this technique is to use the HTML5 track element to specify a captions 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.

The src attribute of the track element is a URL that is the address of the text track data.

The kind attribute of the track element indicates the kind of information in the timed text. captions text tracks provide a text version of dialogue and 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 regions 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=subtitles, instead of kind=captions, and may include additional relevant audio information. It is not best practice to use subtitles 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.

Example 1

A video element for a video in the English language with an English caption track. The captions are provided in the WebVTT format.

  <video poster="myvideo.png" controls>
    <source src="myvideo.mp4" srclang="en" type="video/mp4">
    <track src="myvideo_en.vtt" kind="captions" srclang="en" label="English">
  </video>

See live example

Example 2

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 (vtt) 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.vtt" kind="captions" srclang="en" label="English">
    <track src="myvideo_fr.ttml" kind="captions" srclang="fr" label="French">
  </video>

Resources

• HTML 5, the track element
• Timed Text Markup Language 1
• WebVTT: The Web Video Text Tracks Format
• Captionator Polyfill

Related Techniques

• G87: Providing closed captions

Tests

Procedure

For the video element used to play a video:

1. Check that the video contains a track element of kind captions in the language of the video.

Expected Results

• Check that #1 is true