Research On Multimedia Synchronization For Continuous Media Over The Internet

With recent developments in networking technologies, it is feasible to provide multimedia services such as Internet Protocol TV, Video on Demand, distance learning, videophone and videoconference in broadband networks. The most prominent feature that distinguishes multimedia applications from other data applications is the integration of various media streams that must be presented in a synchronized fashion. 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.The research work in this dissertation carries a rather deep study on multimedia synchronization for continuous media over the Internet, and the major achievements and results are outlined as follows.1. The Chebychev inequality and statistic characterizes of delay jitter are utilized to predict network delay boundary of packet transmission, and based on the prediction a playout control scheme for VoIP is proposed. The scheme makes short-term prediction about current playout delay according to historical trace of network delay and determines the playout times of packets in each talkspurt. Experimental results show that the proposed scheme can adaptively follow the changes of network delay and acquire a tradeoff of playout delay against late packet ratios, furthermore, it can adaptively select the value of k to make late packet ratios below 5%.2. An algorithm of media synchronization is proposed for MPEG2 Software Decoder. It is unnecessary for the algorithm to regulate the values of local system clock in decoder. With audio as master media stream whose playout frame rate is nominal and video as slave stream, the algorithm synchronously initiates to play back them and makes use of presentation time stamp of the media units which have a common time base to synchronize the presentation of video sequence with audio sequence. Experimental results show that the proposed algorithm can acquire media synchronization and meet the requirements of perceptual QoS. The algorithm has been applied in an actual multimedia communication system and achieved favorable performance.3. A feedback control scheme for media synchronization of stored media is proposed. This scheme presents the designing criterias of audio playout buffer size and video playout buffer size that are used to achieve media synchronization. The occupiedlevels of two playout buffers are respectively checked to detect asynchronism. Once an asynchronism occurred, a required corrective transmission frame rate of the corresponding media stream is fed back to the sender to compensate for delay jitter and network anomaly to restore intra-media synchronization. With intra-media synchronization within audio stream and video stream performed, the receiver synchronously initiates to play back them, and then inter-media synchronization between audio and video is required. Experimental results show that the scheme could remarkably decrease the probability of lost media unit and playout delay. The scheme could keep continuous presentation of audio stream and video stream, and require inter-media synchronization between audio and video.4. A playout control scheme for media synchronization of streaming media is proposed from the receiver angle. The scheme adjusts the audio frame length without impairing audio quality according to the occupied level of audio playout buffer and changes the playout frame rate of video according to the occupied level of video playout buffer to achieve intra-media synchronization of audio stream and video stream. With audio as master media stream and video as slave stream, the scheme makes a comparison between the presentation time stamp of the audio frame and the video frame which are played back recently to synchronize the presentation of video sequence with audio sequence. Experimental results show that in the case of an unincreased playout delay the proposed scheme could achieve intra-media synchronization of a single media stream and require inter-media synchronization between audio and video.