Following the development of high-speed networks, intelligent multimedia workstations and large-scale storage device technologies, distributed multimedia information services are now making their appearance. However, many obstacles remain to be overcome before practical, widespread applications of multimedia services can be realized. One key issue is how to integrate continuous media such as audio and video into semantically synchronized multimedia objects in a distributed workstation environment. This paper describes media synchronization and rate control for a multimedia information system capable of providing correct audio and video data output timing while keeping their packet streams regulated. We have developed an efficient audio/video transmission system architecture which takes into account each media's unique characteristics and provides a flexible synchronization mechanism between these different media. In this paper, we introduce three different synchronization methods, namely strict synchronization, relaxed synchronization and silence-detected synchronization. We have implemented these three methods on two different operating system environments: UNIX, using inter-process communication functions, and Mach, using tasks/threads. In order to verify these methods, we have successfully developed a prototype packet audio/video system and performed synchronization accuracy and performance evaluations under various load conditions in both operating environments.