Proposed video element visual-only content has audio track alternative

Description

Non-streaming video elements without audio must have an audio alternative.

Applicability

This rule applies to any non-streaming video element that is visible where the video does not contain audio.

Expectation

The visual information of each test target is available through an audio track.

Assumptions

A mechanism is available to start the video and that the video element is not simply used to display the poster.
The language of each test target can be correctly determined (either programmatically or by analyzing the content), and sufficiently understood.

Accessibility Support

There are no major accessibility support issues known for this rule.

Background

Bibliography

Accessibility Requirements Mapping

G166: Providing audio that describes the important video content and describing it as such
- Learn more about technique G166
- Not required for conformance to any W3C accessibility recommendation.
- Outcome mapping:
  - Any failed outcomes: technique is not satisfied
  - All passed outcomes: technique needs further testing
  - An inapplicable outcome: technique needs further testing

Input Aspects

The following aspects are required in using this rule.

DOM Tree
CSS Styling
Audio output (no link available)
Visual output (no link available)
Language

Test Cases

Passed

Passed Example 1

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This video element, which has no audio, has a separate audio track that describes the visual information.

<html lang="en">
	<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>

	<audio controls>
		<source src="/test-assets/rabbit-video/audio-description.mp3" type="audio/mpeg" />
	</audio>
</html>

Failed

Failed Example 1

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This video element, which has no audio, does not have an audio track describing the visual information.

<html lang="en">
	<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>
</html>

Failed Example 2

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This video element, which has no audio, has a separate audio track that incorrectly describes the visual information.

<html lang="en">
	<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>

	<audio controls>
		<source src="/test-assets/rabbit-video/incorrect-audio-description.mp3" type="audio/mpeg" />
	</audio>
</html>

Inapplicable

Inapplicable Example 1

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This video element has audio.

<html lang="en">
	<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>
</html>

Inapplicable Example 2

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This video element is not visible.

<html lang="en">
	<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" />
	</video>
</html>

Glossary

Non-streaming media element

A non-streaming media element is an HTML Media Element for which the duration property is not 0.

Outcome

An outcome is 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: Implementations 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

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.

For more details, see examples of visible.

Implementations

There are currently no known implementations for this rule. If you would like to contribute an implementation, please read the ACT Implementations page for details.

Changelog

This is the first version of this ACT rule.