Understanding Success Criterion 1.2.4 [Audio Description]
1.2.4 Audio description of video is provided for prerecorded synchronized media. (Level AA)
Intent of this Success Criterion
The intent of this success criterion is to provide people who are blind or visually impaired access to the visual information in a synchronized media presentation. The audio description augments the audio portion of the presentation with the information needed when the video portion is not available. During existing pauses in dialogue, audio description provides information about actions, characters, scene changes, and on-screen text that are important and are not described or spoken in the main sound track.
Note 1: For 1.2.2, 1.2.3, and 1.2.7, if all of the information in the video track is already provided in the audio track, no audio description is necessary.
Note 2: 1.2.2, 1.2.4, and 1.2.7 overlap somewhat with each other. This is to give the author some choice at the minimum conformance level, and to provide additional requirements at higher levels. At Level A in SC 1.2.2, authors do have the choice of providing either an audio description or a full text alternative. If they wish to conform at Level AA, under SC 1.2.4 authors must provide an audio description - a requirement already met if they chose that alternative for 1.2.2, otherwise an additional requirement. At Level AAA under SC 1.2.7 they must provide an extended text description. This is an additional requirement if both 1.2.2 and 1.2.4 were met by providing an audio description only. If 1.2.2 was met, however, by providing a text description, and the 1.2.4 requirement for an audio description was met, then 1.2.7 does not add new requirements.
[end add]Specific Benefits of Success Criterion 1.2.4:
People who are blind or have low vision as well as those with cognitive limitations who have difficulty interpreting visually what is happening benefit from audio description of visual information.
Examples of Success Criterion 1.2.4
A movie with audio description.
Describer: A title, "Teaching Evolution Case Studies. Bonnie Chen." A teacher shows photographs of birds with long, thin beaks.
Bonnie Chen: "These photos were all taken at the Everglades."
Describer: The teacher hands each student two flat, thin wooden sticks.
Bonnie Chen: "Today you will pretend to be a species of wading bird that has a beak like this."
Describer: The teacher holds two of the sticks to her mouth making the shape of a beak.
Transcript of audio based on the first few minutes of "Teaching Evolution Case Studies, Bonnie Chen" (copyright WGBH and Clear Blue Sky Productions, Inc.)
Related Resources
Resources are for information purposes only, no endorsement implied.
Techniques and Failures for Success Criterion 1.2.4 [Audio Description]
Each numbered item in this section represents a technique or combination of techniques that the WCAG Working Group deems sufficient for meeting this success criterion. The techniques listed only satisfy the success criterion if all of the WCAG 2.0 conformance requirements have been met.
Sufficient Techniques
G78: Providing a sound track that includes audio description as the primary sound track
G78: Providing a sound track that includes audio description AND associating it with the synchronized media content using one of the following techniques:
Providing audio description in its own sound track (future link) AND merging the description track with the original soundtrack of the synchronized media content at runtime using one of the following techniques
Using SMIL 1.0 to merge a description track with sound track (future link)
Using SMIL 2.0 to merge a description track with sound track (future link)
Common Failures Identified by the Working Group
The following are common mistakes that are considered failures of Success Criterion 1.2.4 by the WCAG Working Group.
(No failures currently documented)
Additional Techniques (Advisory) for 1.2.4
Although not required for conformance, the following additional techniques should be considered in order to make content more accessible. Not all techniques can be used or would be effective in all situations.
Providing audio description in multiple languages in SMIL 1.0 (future link)
Providing audio description in multiple languages in SMIL 2.0 (future link)
Providing audio description for live synchronized media (future link)
Key Terms
- audio description
narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone
Note 1: Audio description of video provides information about actions, characters, scene changes, on-screen text, and other visual content.
Note 2: In standard audio description, narration is added during existing pauses in dialogue. (See also extended audio description.)
Note 3: Also called "video description" and "descriptive narration."
- synchronized media
audio or video synchronized with another format for presenting information and/or with time-based interactive components