A Composable Architecture for Scripting Multimedia Network Applications

A common approach to experimental multimedia network applications is to structure a range of media tools as independent monolithic applications. In this approach, every change must be incorporated into the appropriate applications, requiring each to be entirely recompiled and then redistributed to users. To simplify this procedure, we decompose the tools into reusable and flexible components, much like those provided in existing multimedia toolkits, such as Berkeley’s Continuous Multimedia Toolkit and MIT’s VuSystem which offer application developers a set of predefined modular building blocks that can be arranged as sources, sinks, and filters for media-data. With a well-decomposed and easy-to-understand object architecture, application developers can glue together components with simple scripts. Objects can be added or tailored to meet specific needs and then easily reassembled in a plug-and-play environment to create new tools. A clean object decomposition also makes it possible to distribute objects across the network and embed these scripts on web pages, in effect using the web as a platform for executing the scripts, fetching necessary components across the network on demand. In fact, because the component architecture makes the scripts so simple, they can be be dynamically generated, customized, and returned by a web server. In summary, this component architecture makes it possible to replace the monolithic applications that were more difficult to frequently modify and maintain with short scripts that are both easy to develop and use. In this report, we first describe a composable object architecture for multimedia networking, outlining its core components. We explain how shortcomings in the composability of existing tools, including ineffective overuse of the class hierarchy, can make the tools difficult to integrate. Overcoming these challenges by refining the object architecture, we are able to demonstrate the intended reusability, flexibility, and extensibility of the toolkit by effectively using it to construct high-level components for a multimedia conferencing tool designed for remote participation in MBone sessions.