US Patent 7631326 Synchronization mechanism for multimedia captioning and audio description

A method for outputting supplemental media streams with a main media stream is presented. The method monitors for triggering events and, upon detecting a triggering event, causes one or more supplemental media streams associated with the triggering event to output. The associated supplemental media streams may be output either synchronously or asynchronously with the main media stream. Synchronous supplemental media streams are output concurrently with the main media stream. Asynchronously output supplemental media streams suspend the main media stream while they are output and terminate any currently outputting supplemental media streams. A supplemental media stream may cause a conditional triggering event to trigger a second supplemental media stream to output synchronously with the first. A second main media stream with associated supplemental media streams may be output asynchronously as a compiled supplemental media stream in connection with a first main media stream.