SIA-R27`<video>` element auditory content has accessible alternative

Accessibility requirements

This rule tests conformance of the following accessibility requirements:

This rule checks that <video> elements have an alternative for information conveyed through audio.

This rule applies to every prerecorded <video> element that is visible, where the video contains audio.

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

This rule assumes that the video element is used to play a video (for example, not only used to display an image), and that there is a mechanism to start the video.
This rule assumes that the language of each test target can be correctly determined (either programmatically or by analyzing the content), and sufficiently understood.

This rule has no known accessibility support concerns.