Continuous media synchronization in distributed multimedia systems

Abstract

Future integrated networks are expected to offer a variety of multimedia services, some of which may involve recording and playback of multiple media strands such as video and audio. Media synchronization, which refers to the temporal coordination of the playback of multiple media strands, is the subject matter of this paper. We compare the requirements for media synchronization against those of clock synchronization and argue that clock synchronization may not be necessary, sufficient or desirable for ensuring media synchronization of pre-recorded media strands. We present a synchronization technique targeted for environments in which non-deterministic variations exist in network delays and in the rates of recording and playback. In this technique, at the time of recording, temporal relationships among media strands are recorded in the form of relative time stamps. In order to facilitate synchronization, at the time of playback, the display sites transmit lightweight feedback units back to synchronizer nodes, concurrently with playback of media units. Using these feedback units, the synchronizers estimate playback times of media units of different media strands and readjust playback so as to enforce synchronization.