Abstract

The MPEG-4 VM8 source rate control use both the frame-based and multiple video object (MVO)-based encoding methods to generate video sources toward a target rate. To incorporate the network conditions, we propose an adaptive MPEG-4 quality control mechanism to overcome various congestion situations of IP network for maintaining the quality of MPEG-4 video source. The mechanism composes of network monitoring unit (NMU) at the encoder end and quality feedback unit (QFU) at the decoder end. Based on the network condition represented by the packet loss rate, the mechanism adjusts the encoding output bitrate dynamically. We verify and simulate the proposed adaptive quality mechanism under various congestion conditions. In frame-based adaptive quality control the frame output bitrate is adjusted by changing the value of quantization parameter instead of decreasing the overall target bitrate directly. In MVO-based adaptive quality control we use feedback to stop error propagation of MVO shape coding rapidly. Moreover, we utilize the object scalability property to protect the significant objects by high priority transmission. Simulation results show that either frame-based or MVO-based adaptive quality control mechanism improves the average PSNR more remarkably than no quality control under the heavy congestion network condition with a packet loss rate 20%. The improvement of average PSNR is in the range from 1.27 to 2.16 dB.