Proposed video element visual-only content has accessible alternative

Description

This rule checks that video elements without audio have an alternative available.

Applicability

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

Expectation

For each test target, the outcome of at least one of the following rules is passed:

Assumptions

A mechanism is available to start the video and 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

The HTML video element can also have a track element that provides an audio description. This should provide assistive technologies with a timed text description of visual information in a video. However, there is no native support in any major browser for this technique. Technique H96: Using the track element to provide audio descriptions can not be relied upon to conform to 1.2.1: Audio-only and Video-only (Prerecorded).

Background

Bibliography

Accessibility Requirements Mapping

1.2.1 Audio-only and Video-only (Prerecorded) (Level A)
- Learn more about 1.2.1 Audio-only and Video-only (Prerecorded)
- Required for conformance to WCAG 2.0 and later on level A and higher.
- Outcome mapping:
  - Any failed outcomes: success criterion is not satisfied
  - All passed outcomes: success criterion needs further testing
  - An inapplicable outcome: success criterion needs further testing
G159: Providing an alternative for time-based media for video-only content
- Learn more about technique G159
- 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
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 Rules

Outcomes of the following rules are required as input for this rule.

Test Cases

Passed

Passed Example 1

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This video element, which has no audio, has a text transcript available on the same page. Thus, it passes rule Video Element Visual-Only Content Has Transcript.

<html lang="en">
<video controls>
  <source src="/test-assets/rabbit-video/silent.mp4" type="video/mp4"></source>
  <source src="/test-assets/rabbit-video/silent.webm" type="video/webm"></source>
</video>
<p>The above video shows a giant fat rabbit climbing out of a hole in the ground.
He stretches, yawns, and then starts walking.
Then he stops to scratch his bottom.</p>
</html>

Passed Example 2

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This video element, which has no audio, has a separate audio track that describes the visual information. Thus, it passes rule Video Element Visual-Only Content Has Audio Track Alternative.

<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>

Passed Example 3

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This video element, which has no audio, is a media alternative for the text in the page and labeled as such. Thus, it passes rule Video Element Visual-Only Content Is Media Alternative For Text.

<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-with-captions-silent.mp4" controls></video>
</html>

Failed

Failed Example 1

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This video element, which has no audio, has a transcript which does not convey the information included in the video-only content. The transcript is available through a link on the same page.

<html lang="en">
<video controls>
  <source src="/test-assets/rabbit-video/silent.mp4" type="video/mp4"></source>
  <source src="/test-assets/rabbit-video/silent.webm" type="video/webm"></source>
</video>
<a href="/test-assets/rabbit-video/incorrect-transcript.html">Transcript</a>
</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>

Failed Example 3

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This video element, which has no audio, is a media alternative for the text in the page but it is not labeled as such.

<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-with-captions-silent.mp4" controls></video>
</html>

Failed Example 4

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This video element, which has no audio, has a track element with descriptions. The description track is not supported.

<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>

Inapplicable

Inapplicable Example 1

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This video element has audio.

<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>

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>

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.