Terry,
The basic accessibility requirement for any multimedia content is that where it requires the use of a plugin, or presents information that is not available in a more acessible format, a text alternative should be provided. In terms of video or audio streaming, this will generally take the form of a plain text transcript or storyboard. In other words...
'Provide content that, when presented to the user, conveys essentially the same function or purpose as auditory or visual content.' - Guideline 1, W3C Web Accessibility Initiative guidelines for accessible content - http://www.w3c.org/WAI
There are various more sophisticated ways of presenting the alternative content, and there is some work being done on being able to provide signed interpretations of multimedia content on the fly. In the short-term, however, a text transcript remains the most accessible (and easiest to implement) alternative.
As for the video format, there is guidance about this in the technical standards. Video content must be made available in either the appropriate MPEG format (MPEG-1, MPEG-2 or MPEG-4) or one of the proprietary formats - AVI, ASF or Quicktime. As a general rule of thumb, it is usually a good idea to make use of a format that is widely supported by a variety of different players. This helps avoid the situation we have seen with some platforms, where previously freely available plugins have subsequently introduced charges in later versions. With this in mind, I would generally go with MPEG.
The final thing to remember is that some text descriptions are better than others. In other words, just putting up a simple text description of, say, the speech content of a video, will not necessarily convey to the visually impaired user the full content of the multimedia experience. Always try and create alternative text that provides a complete description of what is happening and, if you have time, evaluate the descriptions with users and incorporate their findings.
Hope that helps!
Nick
Nick Poole
ICT Adviser
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