2.1.4 Consideration for the principle perceivable

Consideration for synchronized text

If you have ever watched a television show in which the sound track was a second or two out of sync with the action, then you will have some idea of how annoying that can be with captions or descriptions of video. When the words or sounds and the accompanying visuals relate to each other in important ways any mismatch between the two can be annoying at best and misleading at worst. When you provide any supporting or accompanying information such as closed or open captions, or video description to make web content more perceivable, it must be accurately related to the action. The WCAG 2.0 guidelines refer to this as time-sensitive synchronized media.

Considerations for captioning

Digital cable receivers often have difficulties with their audio stream. The sound track switches on and off for lengths of time at random intervals. In many cases, the captioning service that is provided for much of the Canadian broadcast day, allows viewers to continue to enjoy the show. If the captioning is good, the audience can follow the dialog with the intermittent sound either on or off. If the captioning is bad with lots of spelling and interpretive errors, or if the captions aren't properly synchronized with the action, the audience may get confused and switch off.

When viewers are deaf, deafened or hard of hearing, captioning is always needed, and accuracy and proper synchronization of the captions is essential. Today, the web is fast becoming the delivery channel of choice for all types of media. Whether it is live or recorded, streaming media or downloadable audio or video files, the need to be able to understand and enjoy the content with or without the ability to hear the audio portion is important.

Considerations for video descriptions

Video description is typically a separate audio track that, in suitable pauses or blank areas of the spoken sound track, inserts a brief description of the important action or surroundings. These brief descriptive insertions need to be closely associated with the visual actions and the related spoken dialog otherwise important context will be lost to the listener. If the video description track is done with text instead of recorded audio, then it might be read aloud by a screen-reading application.

Visit the following links to access more specific information on coding techniques related to the creation of perceivable Web content including alternative text, synchronized text, captioning and video description:

WCAG 2.0 — Table of Contents [ http://www.w3.org/TR/WCAG20/ ]

WCAG 2.0 — Guidelines for Principle 1 — Perceivable [ http://www.w3.org/TR/WCAG20/#perceivable ]

Understanding and Implementing WCAG 2.0 [ http://www.w3.org/TR/UNDERSTANDING-WCAG20/ ]

Techniques and Failures for Web Content Accessibility Guidelines [ http://www.w3.org/TR/WCAG20/-TECHS/ ]

Customizable Quick Reference to WCAG 2.0 Success Criteria [ http://www.w3.org/WAI/WCAG20/quickref/ ]

Refer also to Section 6.0 — Resources.