The successful synchronization of multimedia content, especially audio and video, is essential to accessible web-based communication and cooperation. Understandable media is therefore media synchronized to very specific limits, which have been investigated in multiple research studies. By clarifying the parameters of adequate synchronization we can influence the development of future technologies, specifications, and accessibility guidelines. In doing so, we can help to enhance the accessibility and usability of Web-based multimedia for everyone.
Providing an accessible multimedia experience requires that distinct media resources be presented concurrently. However, an absolutely simultaneous presentation of different media tracks is often not possible. The timing and presentation of each resource must support comprehension. Put differently, the distinct media resources must not be allowed to drift too far out of synchronization.
In preparing this document, we reviewed the research literature to clarify the ranges of acceptable tolerances. This is important, as slips outside these ranges can cause loss in comprehension for the user. Research shows that people will not understand media when its components fall outside specific synchronization tolerances. For comprehension of media across multiple formats, accessible multimedia requires that its component parts remain within research validated synchronization limits. These components may be audio, video, captions, sign language interpretation, and descriptions of video content.
The Accessible Platform Architectures (APA) Working Group decided to publish Synchronization Accessibility User Requirements as a W3C Group Note following a detailed investigation of synchronization tolerances based on the available research literature and input from wide public review of earlier drafts of the document. The document seeks to answer such questions as the following. How much delay can occur between any related audio and video tracks? What are acceptable tolerances between speech and captions before comprehension is adversely affected? To find out, the Research Questions Task Force examined what timing tolerances are appropriate in different circumstances and for different components of accessible multimedia.
The findings are summarized in Synchronization Accessibility User Requirements, now published as a W3C Group Note. Ultimately, the results are expected to be considered in the development of web technologies for multimedia. They are also of interest for purposes of future development of W3C WAI accessibility guidelines. In addition, this work is relevant to multimedia systems, including real-time communication applications. It broadly benefits all users of multimedia content, for whom lip reading, descriptions of video, and captions are useful features in specific contexts such as noisy environments or situations in which visual attention is occupied elsewhere. There are particular benefits to some people with disabilities, for whom these features of multimedia are a necessity in all situations.