Today, multimedia system are still widely realized as monolithic systems. But building such applications using Service-Oriented Architectures -- especially for the Processing and Delivery of continous Multimedia data streams -- has been a controversial topic since years. As a result, applications in the multimedia domain cannot yet benefit from Web service architectures. Thus, building and maintaining large-scale multimedia applications remains a difficult, costly, time-consuming and challenging problem. In this paper we present our approach for building largescale multimedia systems and compare it with the current state of the art, concentrating on the selection and validation of multimedia service composition.