Audio descriptions provide additional information about what is visible on the screen. This allows video content to be accessible to those with visual disabilities. Audio descriptions are helpful on the web if visual content in web video provides important content not available through the audio alone.
A standards-based language used by Quicktime and RealPlayer to control the layout and presentation of visual and audible items. SMIL is used to control the display, positioning, and timing of captions and audio/video multimedia. The captions themselves are stored in a Text Track file if you're using Quicktime or a RealText file if you're using RealPlayer.
Microsoft's technique for adding captions for Windows Media Player. A SAMI file contains the text to be displayed within the captions and information that synchronizes individual caption displays to the multimedia presentation.