In the summer of 1998, Microsoft introduced Synchronized Accessible Media Interchange or SAMI for the purpose of adding closed captioning to multimedia content to be viewed with Microsoft Windows Media Player. Demonstrations and sample multimedia files are available at the SAMI site. Some of the variations on closed captions are very interesting, such as using highlighting in a transcript as a captioning display methodology.
Here is an example from the SAMI site where the transcript is displayed in a window under the video, and the current text, that is the caption, is highlighted in the displayed transcript.
SAMI is an HTML-like language that provides "layout" of a multimedia file, and that layout includes timing of the events for displaying or, in the example above, highlighting of the current caption. For web pages, you can view the source file, View > Source, or Source > View Source in the Web Accessibility Toolbar. I haven't found a comparable option when looking at multimedia players for viewing the source of SAMI or, as we will mention in a bit, SMIL files. SAMI files are needed for multimedia content played on Microsoft Windows Media Player.