Multimedia applications handling audio and video data have to obey time characteristics of these media types — for a single stream of multimedia data as well as for the synchronization of related streams. Correctness with respect to time constraints requires mechanisms which lead to favored processing of multi-media operations. CPU scheduling techniques based on the experience from real-time operating systems offer a solution and provide multimedia applications with the ability to meet time-related Quality of Service (QoS) requirements.This presentation starts with an overview on the required Quality of Service for synchronized audio and video streams. Subsequently it describes an implementation of a CPU scheduler designed to run under IBM's AIX. The evaluation of the implementation based on measurements shows that the scheduler is able to support the time requirements of multimedia applications and that such mechanisms are indeed necessary since otherwise deadline violations occur.