Video element audio described


Description

This rule checks that non-streaming video elements have all visual information also contained in the audio.

Applicability

The rule applies to every non-streaming video element that is visible where the video contains audio.

Expectation

The visual information of each test target is available through its audio, or through an audio description track.

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

There are only a few implementations of video players (without third party technologies) that support audio description tracks at the time of writing.

Background

Test Cases

Passed

Passed Example 1

A video element with a voiceover that describes the visual information.

<video controls>
	<source src="../test-assets/rabbit-video/video-with-voiceover.mp4" type="video/mp4" />
	<source src="../test-assets/rabbit-video/video-with-voiceover.webm" type="video/webm" />
</video>

Passed Example 2

A video element with an audio description.

<link rel="stylesheet" href="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-core/ozplayer.min.css">
<link rel="stylesheet" href="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-skin/highlights-blue.css">
<link rel="stylesheet" href="https://ozplayer.global.ssl.fastly.net/3.3/transcript.css">

<figure id="ozplayer-1-container" class="ozplayer-container">
  <div data-controls="stack" class="ozplayer" id="ozplayer-1">
    <video controls="controls" preload="none">
      <source src="../test-assets/rabbit-video.mp4" type="video/mp4"></source>
    </video>
    <audio data-default="default" preload="none">
      <source src="../test-assets/rabbit-video/audio-description.mp3" type="audio/mp3"  />
    </audio>
  </div>
</figure>

<script src="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-core/mediaelement.min.js"></script>
<script src="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-core/ozplayer.free.js"></script>
<script src="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-lang/en.js"></script>
<script src="https://ozplayer.global.ssl.fastly.net/3.3/config.js"></script>

Note: The ozplayer implementation is only an example and is not meant as an endorsment of the ozplayer.

Failed

Failed Example 1

A video element without an audio description.

<video controls>
	<source src="../test-assets/rabbit-video/video.mp4" type="video/mp4" />
	<source src="../test-assets/rabbit-video/video.webm" type="video/webm" />
</video>

Failed Example 2

A video element with an incorrect audio description.

<video controls>
	<source src="../test-assets/rabbit-video/video-with-incorrect-voiceover.mp4" type="video/mp4" />
	<source src="../test-assets/rabbit-video/video-with-incorrect-voiceover.webm" type="video/webm" />
</video>

Failed Example 3

A video element with an incorrect audio description.

<link rel="stylesheet" href="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-core/ozplayer.min.css">
<link rel="stylesheet" href="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-skin/highlights-blue.css">
<link rel="stylesheet" href="https://ozplayer.global.ssl.fastly.net/3.3/transcript.css">

<figure id="ozplayer-1-container" class="ozplayer-container">
  <div data-controls="stack" class="ozplayer" id="ozplayer-1">
    <video controls="controls" preload="none">
      <source src="../test-assets/rabbit-video/video.mp4" type="video/mp4"></source>
    </video>
    <audio data-default="default" preload="none">
      <source src="../test-assets/rabbit-video/incorrect-audio-description.mp3" type="audio/mp3"  />
    </audio>
  </div>
</figure>

<script src="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-core/mediaelement.min.js"></script>
<script src="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-core/ozplayer.free.js"></script>
<script src="https://ozplayer.global.ssl.fastly.net/3.3/ozplayer-lang/en.js"></script>
<script src="https://ozplayer.global.ssl.fastly.net/3.3/config.js"></script>

Note: The ozplayer implementation is only an example and is not meant as an endorsment of the ozplayer.

Inapplicable

Inapplicable Example 1

A video element without audio.

<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>

Inapplicable Example 2

A video element that is not visible on the page.

<video controls style="display: none;">
	<source src="../test-assets/rabbit-video/video.mp4" type="video/mp4" />
	<source src="../test-assets/rabbit-video/video.webm" type="video/webm" />
</video>

Glossary

Outcome

key: outcome

A conclusion that comes from evaluating an ACT Rule on a test subject or one of its constituent test target. An outcome can be one of the three following types:

  • Inapplicable: No part of the test subject matches the applicability
  • Passed: A test target meets all expectations
  • Failed: A test target does not meet all expectations

Note: A rule has one passed or failed outcome for every test target. When there are no test targets the rule has one inapplicable outcome. This means that each test subject will have one or more outcomes.

Note: Implementers using the EARL10-Schema can express the outcome with the outcome property. In addition to passed, failed and inapplicable, EARL 1.0 also defined an incomplete outcome. While this cannot be the outcome of an ACT Rule when applied in its entirety, it often happens that rules are only partially evaluated. For example, when applicability was automated, but the expectations have to be evaluated manually. Such "interim" results can be expressed with the incomplete outcome.

Visible

key: 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.


Changelog

Aug 21, 2019fix: update links to WCAG21 resources (#776)
Aug 21, 2019Editorial changes (#725)
Jul 26, 2019Editorial changes (#702)
Jul 19, 2019chore: run prettier (#688)
Jul 17, 2019fix: test if definition for all referenced glossary terms exist (#634)
Jul 2, 2019chore: Correct various typos (#640)
May 9, 2019Chore: Adapt site to ACT Rules CR format (#547)
May 7, 2019Template update - video element audio described (#531)
Apr 29, 2019chore: rename files and update associations (#489)
Apr 16, 2019chore: add unique id to all rules (#478)
Apr 15, 2019chore: WCAG ACT RULES CG Website Update (#437)
Jan 22, 2019rule: SC 1.2.3 & 1.2.5 Video alternatives (#204)
Nov 12, 2018chore: remove selector `data-rule-target` (#347)
Oct 9, 2018Fix: testcase generation (#296)
Aug 30, 2018Chore: Update test cases format and descriptions (#230)
Aug 2, 2018Rule: SC1-2-3 video-description (#157)
Jun 6, 2018DRAFT: SC1-2-video-element (#106)

Useful Links



Acknowledgements