Abstract: A nonlinear editing system for audio, video and/or other source materials comprises a system to define at least one time line representing the edit, the time line being represented in the editing system as an operator graph. The operator graph includes operators, representing sources and time-based effects, and time varying connections therebetween. For each period of the defined time line wherein the connections do not change, a expression tree comprising a simplified representation of the operators and the connections required to render that portion of the time line is extracted. Each expression tree can be examined to ensure that all of the required sources and/or connections are available to render that portion of the time line in real time and, if this is not the case, a determination can be made of which portions of the expression tree can be pre-rendered to an intermediate result, the intermediate result being substituted into expression tree to provide real time rendering.

Abstract: The present invention concerns a multimedia presentation computer program that includes method and apparatus for sharing presentation functions between portions of the program by means of an interface that is implemented as one or more dynamically linked custom programs that perform one or more functions as the multimedia presentation computer program executes. A number of interface methods in the multimedia presentation computer program are declared and are implemented in the custom program The interface methods of the custom program are made accessible to the multimedia presentation computer program by means of an identifier. A host program within the multimedia presentation computer program communicates with the custom program by means of custom program parameters that at least in part define operation of the custom program. The custom program executes and thereby implements its one or more functions for use by the multimedia presentation computer program.