Proposed Video element visual content has audio description

Description

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

Applicability

This 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.
This rule assumes that the language of each test target can be correctly determined (either programmatically or by analyzing the content), and sufficiently understood.

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

Bibliography

Accessibility Requirements Mapping

G8: Providing a movie with extended audio descriptions
- Learn more about technique G8
- 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
G78: Providing a second, user-selectable, audio track that includes audio descriptions
- Learn more about technique G78
- 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
G173: Providing a version of a movie with audio descriptions
- Learn more about technique G173
- 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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A video element with a voiceover that describes the visual information.

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

Passed Example 2

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A video element with an audio description.

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

Failed

Failed Example 1

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A video element without an audio description.

<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>

Failed Example 2

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A video element with an incorrect audio description.

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

Failed Example 3

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A video element with an incorrect audio description.

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

Inapplicable

Inapplicable Example 1

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A video element without audio.

<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>

Inapplicable Example 2

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A video element that is not visible.

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