Research On Multimedia Synchronization For Continuous Media

With recent developments in networking technologies, it is feasible to provide multimedia services such as video on demand, distance learning, videoconference and multimedia mail via high bandwidth network. Compared with traditional data applications, multimedia services are characterized by the integration of different types of media with at least one time-dependent medium. There are some temporal relationships among the information units of these media streams, which must be maintained during their storage, delivery and presentation. Multimedia synchronization is a special and important quality of service in multimedia systems. As a key technology in multimedia communications, research on multimedia synchronization has received a wide range of attention in the recent years.This paper deals with multimedia synchronization for continuous media, and the main research work and results are listed as follows.1. An algorithm of compensation buffer determination in multimedia systems is presented. Based on the first order and second order statistical analysis of the delay jitter, the buffer size can be determined according to its relationship with perceived QoS. After adopting the Chebyshev and the Chernoff bound, the buffer required can be presented in a simple formula. Simulation results show that our method of buffer determination is effective. With this method, synchronization system can always meet the perceived QoS defined by user. Additionally, it also has high buffer utilization and satisfied end to end delay.2. A feedback control scheme for intra-media synchronization of stored multimedia streams is proposed. The buffer level is checked periodically to detect asynchrony. Once an asynchrony occurred, a required corrective transmission rate is fed back to the source in order to restore synchrony. The criteria of designing buffer size and the rule of the transmission rate regulation are presented. The effect of several parameters on the scheme is also analyzed. Experimental results show that the scheme is able to deal with asynchronies introduced by the variable average delay. The scheme wins an advantage over previous others in decreasing the probability of lost data and keeping good quality of continuous presentation.3. An improved dynamic playout algorithm is proposed in order to keep multimedia playing smoothly, which deals with the problem from the perspective of an end system. In the algorithm, playout rates of multimedia are variable according to the occupied buffer level with an intention of eliminating buffer underflow or overflow.The playout rates are chosen based on the requirement of the intra-rnedia synchronization. To determine the thresholds of the occupied buffer level, two queuing models with different arrivals are established. Based on the analytic results, suitable thresholds can be determined according to the system parameters, including the probability of buffer underflow, the probability of buffer overflow and the average playout rate. The algorithm wins an advantage over Yuang's in VoD (Variance of Discontinuity) and VDoP (Variance of Distortion of Playout). 4. Based on the analysis of Resource Reservation Protocol (RSVP), Real time Transport Protocol (RTF), Real time Control Protocol (RTCP) and Real Time Streaming Protocol (RTSP), a multimedia synchronization control scheme over IP is proposed. It combines RTSP with RSVP to set up and manage reserved-bandwidth streaming sessions that are carried by RTF. After mapping users' synchronization requirements to the network QoS (FLOWSPEC in RSVP), RSVP can reserve resource to guarantee intra-stream synchronization. RTCP control packets can be used to determine the network congestion state and to control the quality of session. Inter-stream synchronization can be achieved by adjusting the process of playout. With this scheme, intra-stream and inter-stream synchronization can be guaranteed in real-time multimedia applications over IP.