STATISTICALLY BASED BUFFER CONTROL POLICIES FOR CONSTANT RATE TRANSMISSION OF COMPRESSED DIGITAL VIDEO

This paper presents an investigation of statistically based approaches to the design of buffer control algorithms for interfacing a compressed digital video source to a constant rate channel. Since video compression techniques such as DPCM or transform coding with Huffman-type statistical encoding are characterized by a variable output bit-rate, rate buffering and adaptive encoding are used to maintain high average image quality, while avoiding buffer overflow events. As a first step to a quantitative methodology for the design and evaluation of adaptive buffer control algorithms, a detailed statistical characterization of the various encoding modes of an example "broadcast quality" intra/interframe DPCM algorithm is obtained from extensive simulation. The statistics presented include simple measures such as the overall encoded rate distributions for each encoding mode (which are useful for general mode selection), as well as more detailed intermode and intramode statistics (which provide useful information for mode switching). Two specific adaptive mode control algorithms are proposed. These are a) the expected "rate policy line" algorithm, driven by conditional intermode expectation statistics, and b) the "constant overflow probability" algorithm driven by conditional intramode distributions. Using simulation over a large set of representative images, the performance of the proposed statistically based algorithms is compared to that of a conventional buffer-level-based control heuristic which does not require source characterization. It is demonstrated that the proposed buffer control methods potentially provide substantial performance improvement over unaided heuristics, without significantly increasing implementation complexity.