FEEDBACK TECHNIQUES FOR CONTINUITY AND SYNCHRONIZATION IN MULTIMEDIA INFORMATION-RETRIEVAL

Future advances in storage and networking technologies will make it fe asible to build multimedia on-demand information servers capable of pr oviding services similar to those of a neighborhood videotape rental s tore over metropolitan area networks, Such multimedia information serv ers must not only support retrieval of continuous media units (such as video frames and audio samples), but also preserve synchrony among pl ayback of the different media components constituting a multimedia obj ect. We develop techniques for supporting continuous and synchronous r etrieval from multimedia servers. We present feedback techniques by wh ich, during retrieval of multimedia objects from a multimedia server t o mediaphones, the multimedia server uses lightweight messages called feedback units transmitted periodically back to it (by mediaphones) to detect impending discontinuities as well as asynchronies at mediaphon es. The multimedia server then preventively readjusts media transmissi on so as to avoid either anomaly, and steers the mediaphones back to s ynchrony. Given the available buffer sizes at mediaphones and the maxi mum tolerable asynchrony, we present methods to determine the minimum rate at which feedback units must be transmitted so as to maintain bot h continuity and synchronization. These feedback techniques remain rob ust even in the presence of playback rate mismatches and network delay jitter, and their initial simulation for video-audio playback yields a feedback rate of one per 1,000 media units to keep the asynchrony wi thin 250ms, showing that the overhead due to feedback transmission is very small. The constant rate feedback techniques developed in this ar ticle form the basis of a prototype on-demand information server being developed at the UCSD Multimedia Laboratory.