Proposed Audio and visuals of video element have transcript
Description
This rule checks that non-streaming video
elements have all audio and visual information available in a transcript.
Applicability
This rule applies to every non-streaming video
element that is visible.
Expectation
The visual information of each test target is available through a text transcript that is visible, included in the accessibility tree, and is either on the page or linked.
Note: A “text transcript” in the context of this rule is defined in WCAG 2 as an alternative for time based media.
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
There are no accessibility support issues known.
Background
Bibliography
- Understanding Success Criterion 1.2.3: Audio Description or Media Alternative (Prerecorded)
- Understanding Success Criterion 1.2.8: Media Alternative (Prerecorded)
- G78: Providing a second, user-selectable, audio track that includes audio descriptions
- G173: Providing a version of a movie with audio descriptions
- G203: Using a static text alternative to describe a talking head video
Accessibility Requirements Mapping
1.2.8 Media Alternative (Prerecorded) (Level AAA)
- Learn more about 1.2.8 Media Alternative (Prerecorded)
- Required for conformance to WCAG 2.0 and later on level AAA.
- 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
- Any
G69: Providing an alternative for time based media
- Learn more about technique G69
- 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
- Any
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
A video element with a text transcript on the same page.
<html lang="en">`
<video controls>
<source src="/test-assets/rabbit-video/video.mp4" type="video/mp4"></source>
<source src="/test-assets/rabbit-video/video.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, yaws, and then starts walking.
Then he stops to scratch his bottom.</p>
</html>
Passed Example 2
A video element with a link to a text transcript on a different page.
<html lang="en">`
<video controls>
<source src="/test-assets/rabbit-video/video.mp4" type="video/mp4"></source>
<source src="/test-assets/rabbit-video/video.webm" type="video/webm"></source>
</video>
<a href="/test-assets/rabbit-video/transcript.html">Transcript</a>
</html>
Failed
Failed Example 1
A video element with an incorrect text transcript on the same page.
<html lang="en">`
<video controls>
<source src="/test-assets/rabbit-video/video.mp4" type="video/mp4"></source>
<source src="/test-assets/rabbit-video/video.webm" type="video/webm"></source>
</video>
<p>The above video shows a giant fat dog climbing out of a hole in the ground.
He stretches, yaws, and then starts walking.
Then he stops to scratch his bottom.</p>
</html>
Failed Example 2
A video element with a link to an incorrect text transcript on a different page.
<html lang="en">`
<video controls>
<source src="/test-assets/rabbit-video/video.mp4" type="video/mp4"></source>
<source src="/test-assets/rabbit-video/video.webm" type="video/webm"></source>
</video>
<a href="/test-assets/rabbit-video/incorrect-transcript.html">Transcript</a>
</html>
Inapplicable
Inapplicable Example 1
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>
<source src="/test-assets/rabbit-video/video.webm" type="video/webm"></source>
</video>
<a href="/test-assets/rabbit-video/transcript.html">Transcript</a>
</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
ofnone
; or - has an
aria-hidden
attribute set totrue
Note: Contrary to the other conditions, the visibility
CSS property may be reverted by descendants.
Note: The HTML standard suggests setting the CSS display
property to none
for elements with the hidden
attribute. While not required by HTML, all modern browsers follow this suggestion. Because of this the hidden
attribute is not used in this definition. In browsers that use this suggestion, overriding the CSS display
property can reveal elements with the hidden
attribute.
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.
For more details, see examples of visible.
Rule Versions
This is the first version of this ACT rule.
Implementations
This section is not part of the official rule. It is populated dynamically and not accounted for in the change history or the last modified date.