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Proposed Video element visual-only content has description track

Deprecated

This rule has been deprecated as descriptions tracks were removed in #1665 as a way to provide video alternative. This rule is not maintained anymore and should not be used.

Description

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

Applicability

This rule applies to every non-streaming video element that is visible where the video does not contain audio and contains a track element with a kind attribute value of descriptions.

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.

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 technologies. Video players may be able to work around the lack of support for the description track by using aria-live but few do this today.

Background

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.

Bibliography

Accessibility Requirements Mapping

Input Aspects

The following aspects are required in using this rule.

Test Cases

Passed

Passed Example 1

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This video element, which has no audio, has a track element with descriptions.

<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" />
		<track kind="descriptions" src="/test-assets/rabbit-video/descriptions.vtt" />
	</video>
</html>

Failed

Failed Example 1

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This video element, which has no audio, has a track element with incorrect descriptions.

<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" />
		<track kind="descriptions" src="/test-assets/rabbit-video/incorrect-descriptions.vtt" />
	</video>
</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" />
		<track kind="descriptions" src="/test-assets/rabbit-video/descriptions.vtt" />
	</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" />
		<track kind="descriptions" src="/test-assets/rabbit-video/descriptions.vtt" />
	</video>
</html>

Inapplicable Example 3

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This video element, which has no audio, does not have a track element.

<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>

Glossary

Attribute value

The attribute value of a content attribute set on an HTML element is the value that the attribute gets after being parsed and computed according to specifications. It may differ from the value that is actually written in the HTML code due to trimming whitespace or non-digits characters, default values, or case-insensitivity.

Some notable case of attribute value, among others:

This list is not exhaustive, and only serves as an illustration for some of the most common cases.

The attribute value of an IDL attribute is the value returned on getting it. Note that when an IDL attribute reflects a content attribute, they have the same attribute value.

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:

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.

Rule Versions

This is the first version of this ACT rule.

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