Performance of Inter-Media Synchronization in Distributed and Heterogeneous Multimedia Systems

Abstract Future multimedia environments are expected to be distributed and heterogeneous. In such environments, media sites ranging from sophisticated workstations to simple media capture and display subsystems such as ISDN videophones and audiophones (together referred to as Mediaphones ) that lack the capability to run clock synchronization algorithms will be connected directly to the network. Towards such environments, we develop mechanisms and protocols for synchronous access to multimedia services over integrated networks. In the inter-media synchronization technique we present, for facilitating synchronous retrieval, a multimedia server computes at the time of recording of a multimedia object a range of relative temporal positions or stamps (called an RTS interval ) for each media unit that it receives from mediaphones. During playback, the multimedia server detects RTS mismatches between media with the help of feedback messages transmitted back by the mediaphones, and steers the mediaphones back to synchrony. We propose predictive policies for resynchronization and compare their performance for video/audio playback with other resynchronization policies, such as conservative, aggressive, and probabilistic. These performance studies reveal that predictive policies perform uniformly well at all levels of asynchrony, unlike their conservative and aggressive counterparts. Moreover, in most cases, predictive policies match probabilistic policies in effectiveness, without imposing the same computational demands as the probabilistic policies.