Captioning for Windows Media
http://www.webaim.org/techniques/captions/windows/

WebAIM
2003

Abstract:

Windows Media Player adds captions using Microsoft's Synchronized Accessible Media Interchange (SAMI). SAMI, like SMIL, which is used by Quicktime and RealPlayer, is an XML-based text language. A SAMI file contains the captions and definitions for how and when the captions should display.