Synchronization loss and concealment mechanisms in distributed multimedia application

International audienceOne of the fundamental problems in the domain of distributed multimedia application is the synchronization of the communication elements. Multimedia data is defined as bundles composed of several streams (video, audio or text streams). A stream can be defined as a sequence of information units (IU). Intra-synchronization binds IUs of the same stream with ordered or temporal constraints (e.g. one image each 1/25th second), whereas inter-synchronization binds streams of the same bundle (e.g. lip synchronization). In the network environment, three specific phenomena may produce synchronization loss : load variation, jitter, or packet loss. Based on single data stream, usual mechanisms used to preserve synchronization do not work well with multimedia streams. In this paper, we present the synchronization services required by distributed multimedia applications. We propose a formal definition of inter-stream and intra-stream synchronization. We present the impact of intra or inter-stream synchronization loss. We show how to use the specification of synchronization constraints to propose a concealment mechanism. After a synchronization loss, depending on the type of the constraints of the multimedia bundle and streams, appropriated actions are proposed to achieve synchronization recovery