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Description

This rule checks that description tracks that come with non-streaming video elements, without audio, are descriptive.

Test Procedure

Applicability

The rule applies to any non-streaming video element visible where the video doesn’t contain audio and does contain a track element with a kind="descriptions" attribute.

Expectation

The visual information of each test target is described with a description track element that has the same language as the video or the same language as the page.

Note: Multiple description track elements may be useful for different languages, but at least one must match the language of the video or the language of the page.

Assumptions

This rule assumes that a mechanism is available to start the video and that the video element is not simply used to display the poster.

Accessibility support

Currently the description track is not supported by most assistive technology. Video players may be able to work around the lack of support for the discription track by using aria-live but few do this today.

Background

Test Cases

Passed

Pass example 1

A video only element with a track element that contains descriptions.

Code Snippet:
 <video controls>
  <source src="../test-assets/rabbit-video/silent.mp4" type="video/mp4" />
  <source src="../test-assets/rabbit-video/silent.webm" type="video/webm" />
  <track kind="descriptions" src="rabbit-video-descriptions.vtt" />
</video>
 
Example Output: Open in a new tab/ window

Failed

Fail example 1

A video only element with a track element that contains incorrect descriptions.

Code Snippet:
 <video controls>
  <source src="../test-assets/rabbit-video/silent.mp4" type="video/mp4" />
  <source src="../test-assets/rabbit-video/silent.webm" type="video/webm" />
  <track kind="descriptions" src="rabbit-video-incorrect-descriptions.vtt" />
</video>
 
Example Output: Open in a new tab/ window

Inapplicable

Inapplicable example 1

A video only element without a track element.

Code Snippet:
 <video controls>
  <source src="../test-assets/rabbit-video/silent.mp4" type="video/mp4" />
  <source src="../test-assets/rabbit-video/silent.webm" type="video/webm" />
</video>
 
Example Output: Open in a new tab/ window

Inapplicable example 2

A video only element that is not visible on the page.

Code Snippet:
 <video controls style="display: none;">
  <source src="../test-assets/rabbit-video/silent.mp4" type="video/mp4" />
  <source src="../test-assets/rabbit-video/silent.webm" type="video/webm" />
  <track kind="descriptions" src="rabbit-video-descriptions.vtt" />
</video>
 
Example Output: Open in a new tab/ window

Inapplicable example 3

A video element with audio.

Code Snippet:
 <video controls>
  <source src="../test-assets/rabbit-video/video.mp4" type="video/mp4" />
  <source src="../test-assets/rabbit-video/video.webm" type="video/webm" />
  <track kind="descriptions" src="rabbit-video-descriptions.vtt" />
</video>
 
Example Output: Open in a new tab/ window

Glossary

Visible

Content perceivable through sight.

Content is considered visible if making it fully transparent would result in a difference in the pixels rendered for any part of the document that is currently within the viewport or can be brought into the viewport via scrolling.

Content is defined in WCAG.

Test Aspects

Test aspects are defined as part of the ACT Rules format 1.0.
  • DOM Tree

  • CSS Styling

  • Audio output

  • Visual output

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