<video> elements must have an audio description <track>

Rule ID: video-description
Ruleset: axe-core 3.2
User Impact: Critical
WCAG: 1.2.5
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Compliance Data & Impact

User Impact

Disabilities Affected

  • Blindness

Requirement(s)

  • WCAG 2.1 (AA): MUST
  • Section 508: MUST
  • WCAG 2.0 (AA): MUST

WCAG Success Criteria

  • 1.2.5 Audio Description (Prerecorded)

Section 508 Guidelines

  • 1194.22 (b) Multimedia presentation alternatives synchronization

How to Fix the Problem

The purpose of audio description is to fill gaps in dialogue with a narrator describing what is happening visually. The soundtrack containing the audio description of the visual information can be an alternate soundtrack that the user can choose, or it can be the standard sound track that everyone hears.

Ensure that all video elements have audio descriptions that provide all relevant information that dialogue cannot. Examples of relevant information aside from dialogue include facial expressions and scenes.

The following code shows how to add two different audio descriptions - one in English and one in Spanish:

<video width="300" height="200">
    <source src="myVideo.mp4" type="video/mp4">
    <track src="audio_desc_en.vtt" kind="descriptions" srclang="en" label="english_description">
    <track src="audio_desc_es.vtt" kind="descriptions" srclang="es" label="spanish_description">
</video>

The src attribute gives the name of the audio description file. The kind attribute describes the contents of the file. The srclang attribute specifies the language of the file using the appropriate HTML language code. The label attribute provides a name for the audio description. None of these attributes, aside from src, are required. Nevertheless, they are highly recommended because they increase clarity.

Why it Matters

While blind people can hear the audio content of videos with no issue, they miss visual aspects of films such as facial expressions and scenes. Many things happen in movies that are completely visual, with no auditory component. For example, a person can make a facial expression, but not say any words. The camera can show a mountain scene, but no one in the movie says "this is a mountain scene." There is much visual information that blind people miss completely without audio. Audio descriptions are the solution to make visual information in movies accessible to blind people.

If there is no accompanying narration or dialog to explain the visual activity, blind people don't know what's happening. To make that kind of video accessible to a blind person, you need to provide a version of the video with audio descriptions. Audio descriptions are a recording of a person explaining the visual aspects of the video that isn't in the video's original dialog or narration. Audio description works best when users can turn it on or off, or when there is a separate version of the video with audio descriptions for blind users, in addition to the original version without audio descriptions.

Rule Description

The HTML5 video element must have an audio description track to provide blind users with information the dialogue does not.

The Algorithm (in simple terms)

Ensures video elements have audio descriptions.

Resources

Refer to the complete list of axe 3.2 rules.

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