Distributed multimedia applications combine the advantage of distributed computing with the capability of processing discrete and continuous media in an integrated fashion. The development of multimedia applications in distributed environments requires specific abstractions and services, which are usually not provided by generic operating systems. Those services are typically realized by software components, often referred to as middleware. The CINEMA (Configurable INtEgrated Multimedia Architecture) project aims at the development of powerful abstractions for multimedia processing in distributed environments. This paper presents a flexible mechanism for the dynamic configuration of applications. The proposed mechanism allows for the definition of arbitrary complex flow graphs connecting various types of multimedia processing elements. Further, processing elements can simply be composed from other ones to provide higher levels of abstraction. We also propose the abstraction of a clock hierarchy to permit grouping, controlling, and synchronization of media streams. An appealing property of this abstraction is that it harmonizes well with component nesting.