An invention for specifying and synchronously executing an extensible set of events along a single timeline is disclosed. More specifically, an invention for specifying an extensible set of multimedia events within an HTML document and for synchronously invoking the specified events along a single timeline within a Web environment is disclosed. First, a plurality of multimedia events are specified, with each event having a single or plurality of scheduled time(s) on the timeline for its invocation. After the playing of the timeline is started, events from the extensible set of events are executed at their respective predetermined time(s). Furthermore, an arbitration mechanism is provided for determining the order to execute a plurality of events scheduled to be executed at the same time, and a drop threshold mechanism is provided for not executing an event when its actual execution time has exceeded its scheduled execution time by more than a specified window of execution.