Proposed video element content is media alternative for text

Description

This rule checks non-streaming video is a media alternative for text on the page.

Applicability

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

Expectation 1

All the information contained in each test target is available as text that is visible and included in the accessibility tree.

Expectation 2

Each test target is labeled as a video alternative for text on the page. This label is visible and included in the accessibility tree.

Note: The term label does not refer to the label element.

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 no major accessibility support issues known for this rule.

Background

Bibliography

Accessibility Requirements Mapping

This rule is not required for conformance.

Input Aspects

The following aspects are required in using this rule.

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

Test Cases

Passed

Passed Example 1

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A video element that describes some of the text on the same page. The text on the page labels the video as an alternative.

<html lang="en">
	<p>
		Not being able to use your computer because your mouse doesn't work, is frustrating. Many people use only the
		keyboard to navigate websites. Either through preference or circumstance. This is solved by keyboard compatibility.
		Keyboard compatibility is described in WCAG. See the video below to watch the same information again in video form.
	</p>
	<video src="/test-assets/perspective-video/perspective-video.mp4" controls></video>
</html>

Failed

Failed Example 1

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A video element that describes some of the text on the same page. The video contains more information than the text does.

<html lang="en">
	<p>
		Not being able to use your computer because your mouse doesn't work, is frustrating. Either through preference or
		circumstance. This is solved by keyboard compatibility. Keyboard compatibility is described in WCAG. See the video
		below to watch the same information again in video form.
	</p>
	<video src="/test-assets/perspective-video/perspective-video.mp4" controls></video>
</html>

Failed Example 2

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A video element that describes some of the text on the same page. The text is not visible.

<html lang="en">
	<p style="display: none;">
		Not being able to use your computer because your mouse doesn't work, is frustrating. Many people use only the
		keyboard to navigate websites. Either through preference or circumstance. This is solved by keyboard compatibility.
		Keyboard compatibility is described in WCAG. See the video below to watch the same information again in video form.
	</p>
	<video src="/test-assets/perspective-video/perspective-video.mp4" controls></video>
</html>

Failed Example 3

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A video element that describes some of the text on the same page. The text on the page does not label the video as an alternative.

<html lang="en">
	<p>
		Not being able to use your computer because your mouse doesn't work, is frustrating. Many people use only the
		keyboard to navigate websites. Either through preference or circumstance. This is solved by keyboard compatibility.
		Keyboard compatibility is described in WCAG.
	</p>
	<video src="/test-assets/perspective-video/perspective-video.mp4" controls></video>
</html>

Failed Example 4

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A video element that describes some of the text on the same page. The text on the page labels the video as an alternative but the label is not visible.

<html lang="en">
	<p>
		Not being able to use your computer because your mouse doesn't work, is frustrating. Many people use only the
		keyboard to navigate websites. Either through preference or circumstance. This is solved by keyboard compatibility.
		Keyboard compatibility is described in WCAG.
	</p>
	<p style="display: none;">
		See the video below to watch the same information again in video form.
	</p>
	<video src="/test-assets/perspective-video/perspective-video.mp4" controls></video>
</html>

Inapplicable

Inapplicable Example 1

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A video element without audio. The text on the page labels the video as an alternative.

<html lang="en">
	<p>
		Not being able to use your computer because your mouse doesn't work, is frustrating. Many people use only the
		keyboard to navigate websites. Either through preference or circumstance. This is solved by keyboard compatibility.
		Keyboard compatibility is described in WCAG. See the video below to watch the same information again in video form.
	</p>
	<video src="/test-assets/perspective-video/perspective-video-silent.mp4" controls></video>
</html>

Inapplicable Example 2

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A video element that describes some of the text on the same page. The text on the page labels the video as an alternative but the video is not visible.

<html lang="en">
	<p>
		Not being able to use your computer because your mouse doesn't work, is frustrating. Many people use only the
		keyboard to navigate websites. Either through preference or circumstance. This is solved by keyboard compatibility.
		Keyboard compatibility is described in WCAG. See the video below to watch the same information again in video form.
	</p>
	<video src="/test-assets/perspective-video/perspective-video.mp4" controls style="display: none;"></video>
</html>

Glossary

Focusable

An element is focusable if one or both of the following are true:

the element is part of sequential focus navigation; or
the element has a tabindex value that is not null.

Exception: Elements that lose focus during a period of up to 1 second after gaining focus, without the user interacting with the page the element is on, are not considered focusable.

Notes:

The 1 second time span is an arbitrary limit which is not included in WCAG. Given that scripts can manage the focus state of elements, testing the focusability of an element consistently would be impractical without a time limit.
The tabindex value of an element is the value of the tabindex attribute parsed using the rules for parsing integers. For the tabindex value to be different from null, it needs to be parsed without errors.

Included in the accessibility tree

Elements included in the accessibility tree of platform specific accessibility APIs are exposed to assistive technologies. This allows users of assistive technology to access the elements in a way that meets the requirements of the individual user.

The general rules for when elements are included in the accessibility tree are defined in the core accessibility API mappings. For native markup languages, such as HTML and SVG, additional rules for when elements are included in the accessibility tree can be found in the HTML accessibility API mappings (working draft) and the SVG accessibility API mappings (working draft).

For more details, see examples of included in the accessibility tree.

Programmatically hidden elements are removed from the accessibility tree. However, some browsers will leave focusable elements with an aria-hidden attribute set to true in the accessibility tree. Because they are hidden, these elements are considered not included in the accessibility tree. This may cause confusion for users of assistive technologies because they may still be able to interact with these focusable elements using sequential keyboard navigation, even though the element should not be included in the accessibility tree.

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.

Programmatically Hidden

An HTML element is programmatically hidden if either it has a computed CSS property visibility whose value is not visible; or at least one of the following is true for any of its inclusive ancestors in the flat tree:

has a computed CSS property display of none; or
has an aria-hidden attribute set to true

Note: Contrarily to the other conditions, the visibility CSS property may be reverted by descendants.

Note: The HTML standard suggests rendering elements with the hidden attribute with a CSS rule that applies the value none to the CSS property display of the element. Although the suggestion is not normative, known user agents render it according to the suggestion (unless the content specifies another CSS rule that sets the value of the display property). If a user agent does not follow the suggestion, this definition may produce incorrect results for this user agent.

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.