Example for Checkpoint
1.4 - For any time-based multimedia presentation, synchronize equivalent alternatives with the presentation.

A time-based presentation can include any form of multimedia, such as a movie, animation or slide show. Equivalent alternatives to these types of presentations are captions (which provide access to audio tracks) and audio descriptions (which provide access to visual tracks).

We have already explained the need to provide a textual transcript for any audio track (see Checkpoint example 1.1l) or video track (see Checkpoint example 1.1m), and a textual description of the video track (see Checkpoint examples 1.1n and 1.3). However, it must be admitted that a text transcript alone is not the ideal method for providing an equitable experience for persons with disabilities. It is widely accepted that on-screen captioning allows deaf and hard-of-hearing people to more fully appreciate the experience of a movie or multimedia production. An almost-equivalent accommodation for people with sight and hearing is the provision of subtitles during foreign-language films or performances. A separate textual transcript that must be read after the fact does not provide an equivalent experience.

Thus the requirement to synchronize the equivalent alternatives. The caption track is an alternative for deaf or hearing-impaired viewers. The audio-description track is an alternative for people who are blind or visually impaired. Synchronizing these alternatives with the main presentation (that is, the video and/or audio) means that nearly all users will get the best experience and the most information available to them. (Bear in mind that for people who do not have access to multimedia-playback devices, or for people who are deaf-blind, a transcript of both the audio and the audio descriptions is still the best alternative.)

To Checkpoints for Guideline 1.