How do I make multimedia accessible?
Multimedia presentations can be inaccessible to people who are unable to hear their audio content and to people who are unable to see critical information that is presented visually. For a strictly audio presentation, providing a transcript is an adequate accommodation for people with hearing impairments. However, for an audiovisual presentation, a transcript does not provide an equivalent experience, as the presentation's message is dependent upon the simultaneous interaction between its audio and video portions. Even in simple lectures, much of the message is presented through the lecturer's non-verbal communication. For this reason, a text alternative must be synchronized with the multimedia presentation. Similarly, any information that is presented exclusively visually must be verbally described (called "audio description"), and this audio description must also be synchronized with the presentation.
Both the Section 508 standards and the W3C Web Content Accessibility Guidelines agree that "equivalent alternatives for any multimedia presentation shall be synchronized with the presentation."
The National Center for Accessible Media (NCAM) has developed a tool called Media Access Generator (MAGpie) that allows multimedia specialists, publishing
companies, and service providers to add captions, subtitles, and audio descriptions to their work. You can visit their site for more information about
the features of MAGpie 
(http://ncam.wgbh.org/webaccess/magpie/)
and to download a free copy of it.
