Synchronized Accessible Media Interchange Format SAMI is an interchange format used to support closed captioning and audio descriptions to provide extended accessibility to digital media. In its broadest sense, closed captioning provides an alternate and synchronous presentation of some form of media that has time as one of its components. Most usually, this is a transcription of words to accompany a video stream, but it might be extended to include images to accompany a musical stream, translations of spoken audio texts. Most usually, closed captioning appears as a text overlay at the bottom of a screen, but it might be extended to include multiple elements appearing anywhere within a presentation format.
Audio description is apparently less familiar than closed captioning.
It involves some kind of narrative overlay to describe visual materials. Currently, this is interpreted as creating text descriptions of video materials to make the visual materials available to blind audiences. In the past, however, the techniques of audio description were commonly experienced by anyone listening to a sports or live news event on the radio. SAMI is an open interchange format, but in the examples you can view from here, it is realized for the web with the Microsoft ActiveMovie control and Explorer 4.0. At its core, it is a very simple, and it is intended to be something that can be replicated in many environments.