Synchronization problem, which always arises whcn sounds, videos, motion pictures and other nicdia are brought together and integrated into a computcr system, is one of the most important issucs in multimedia communications and applications. In the time-sharing and multi-process erivironmcnt such as UNIX operating system, the traditional synchronization mechanism results in two fatal dcfects, namely, audio discontinuity and out of synchronization between audio and video. In this papcr, a novel mcdia synchronization model in a multi-proccss environment is proposed. Based on this model, a continuous mcdia playback module was implementcd and scnicd as the key component of the two niultimcdia systcms developed in the Communication and Multinicdia Laboratory of National Taiwan Univcrsity. One is the multimedia authoring system which provides interactive VCR-like opcrations and audiohidco editing facilities. The other is a prototype of the VOD (Video On Demand) system which providcs vidco browsing facility. Both systems show that the performance of the proposed synchronization modcl is quite satisfactory.