Research On Adaptive Playout Algorithm For Real-Time Audio In Multimedia Communications

Over the past several years, as the speed of computer, network and multimedia technique increase dramatically, more and more networked multimedia applications proliferate rapidly, such as video conference, distance learning, Voice over IP and Video on Demand. Based on two major research projects: "The Key Techniques of Modern Distance Education: Interactive Real-time Education Software Tools"(Key Science and Technology Item Foundation of China National Education Ministry No.2000175) and "Joint Source and Channel Coding in the Mobile Communication System"(subproject of "Digital Video and Audio Coding, Transmission and Application System", National 863 Project), we discuss, analyze and research the related technologies of audio coding and transmission over networks.The features, applications and protocols of multimedia communications are first introduced in this thesis, and then audio coding is briefly narrated as one of the key technologies in multimedia communications. By analyzing and researching on the packet loss and delay jitter which make the perceived quality of audio degraded severely, a new adaptive algorithm for real-time audio is presented. By monitoring the receiver and playout queues, the algorithm adapts to delay jitter by increasing or decreasing playout delay in response to the thresholds of the length of queues. With adaptive recovery techniques for packet loss, the proposed algorithm can get high perceived quality with few computational complexities. As validated by our experiment results, the adaptive playout algorithm is able to strive for minimizing packet droppings for late-arrival packets under a tightly bounded average playout delay with the acceptable speech quality. Then we introduce the system architecture, network architecture and flow chart of system data in the system of Easy Learning, which is a system of real-time distance learning, and tell how to implement audio coding and transmission in this application. At the same time, the key technologies of audio coding and transmission are discussed, and solutions are addressed accordingly. Finally, the main contributions in this thesis are summarized and some suggestions and directions for the future work are given.