Time-based media under WCAG 2.0

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The WCAG 2.0 guideline in this area is Time-based Media: Guideline 1.2 Provide alternatives for time-based media. Its requirements are summarised below.

Definitions

Time-based media
Media where time is crucial to the presentation of information. Examples are audio and video files, and combinations of both, which are commonly referred to as "multimedia"

Coverage

General principle

The WCAG 2.0 multimedia standards apply to all time-based media created or hosted by agencies.

Requirements and guidance

The information below outlines what's needed to meet the standards, gives some basic development advice and links to implementation resources.

Notes

  1. Media alternative for text: Where a Success Criterion says "except when the media is a media alternative for text and is clearly labelled as such", it means that where a communication is primarily in text, and the multimedia acts mainly as a representation of the text, no captioning is required. An example is video of an executive reading a speech, where the text of the speech is presented on the website as the primary version. Another is where video is provided as an extra option to help people with cognitive, language, or learning disabilities make sense of text (e.g., CAPTCHA).
  2. Options include creating a two versions for each video: a standard version (without accessibility enhancements), and an accessible version (with the enhancements). In some cases this may be simpler than creating a single version in which enhancements can be switched on or off.

1. Audio-only and video-only

WCAG 2.0 requirements

Audio-only and Video-only (Prerecorded): 1.2.1 For prerecorded audio-only and prerecorded video-only media, the following are true, except when the audio or video is a media alternative for text and is clearly labelled as such:

  • Prerecorded Audio-only: An alternative for time-based media is provided that presents equivalent information for prerecorded audio-only content.
  • Prerecorded Video-only: Either an alternative for time-based media or an audio track is provided that presents equivalent information for prerecorded video-only content. Provide an alternative for each.

What's required

Provide an alternative for each. This may be a transcript, or, in the case of video, an audio track describing the video. A transcript suffices in either case.

Advice

Use the original script or screenplay as the basis of the transcript.

Techniques and guidance

WCAG 2.0: Techniques for Audio-only and Video-only (Prerecorded)

2. Audio descriptions

WCAG 2.0 requirements

1.2.5 Audio description is provided for all prerecorded video content in synchronized media. (Level AA)

An audio description is a narration added to the soundtrack to describe important visual details that cannot be understood from the main soundtrack alone.

What's required

Provide an audio description of what's happening in a video, where this description a) is necessary to understanding the action, and b) isn't already present in the audio.

Audio descriptions are required only if the video conveys content visually that is not available in the default audio track. That is, if the video makes sense via the audio track alone, no audio description is needed.

Advice

In most cases, spoken scripts (i.e., monologue, dialogue) will describe action adequately (e.g., training video) and will not require audio descriptions. Because of this, content creators should write scripts to describe action where possible.

If an audio description is required, the easiest option is to provide a second version of the video with an audio track which includes the descriptions.

Techniques and guidance

3. Captions (Prerecorded)

WCAG2.0 requirements

Captions (Prerecorded): 1.2.2 Captions are provided for all prerecorded audio content in synchronized media, except when the media is a media alternative for text and is clearly labelled as such.

What's required

Use captions for speech and important sound effects where sound is necessary to understand what's going on.

Advice

"Media alternative for text": An example is video of an executive reading a speech, where the text of the speech is presented on the website as the primary version. Another is where video is provided as an extra option to help people with cognitive, language, or learning disabilities make sense of text. Agencies should, however, make every attempt to include the enhancements (such as captioning) as suggested.

Techniques and guidance

Captioning
Captioning Flash on YouTube
Software
WCAG 2.0 techniques
Online captioning
  • DotSub is a collaborative captioning project
  • Project ReadOn, and Overstream are two of a number of other sites that also provide captioning functionality (but require that they host the video).

4. Captions (Live)

WCAG 2.0 requirements

Captions (Live): 1.2.4 Captions are provided for all live audio content in synchronized media.

What's required

Provide captions in real time for live multimedia. Note, given the developing nature of live captioning, agencies should email the Web Standards team for more information.

Techniques and guidance