Agnes Yee Ngai

Joint rate control with look-ahead for multi-program video coding

In this paper, we present a new joint rate control algorithm for a multi-program video compression system using MPEG-2 compatible video encoders. The proposed joint rate control is based on both the feedback and look-ahead approaches. It dynamically distributes the channel bandwidth among the program encoders according to the relative complexities of the programs using picture and coding statistics. As opposed to previous works in this area, our algorithm does not restrict the encoders to operate with identical group of pictures (GOP) structures, i.e. the GOP boundaries need not be synchronized among the different encoders. The proposed algorithm allows adaptive distribution of the channel bandwidth among the programs, even at the start of encoding. Furthermore, it assures quick reaction to scene changes, where a feedback approach requires an unavoidable delay. Experimental results show that the proposed joint rate control with look-ahead results in improved picture quality in comparison with a pure feedback approach.

Statistical multiplexing using MPEG-2 video encoders

This paper presents a system for statistical multiplexing of several compressed video programs using MPEG-2-compatible video encoders. We propose a new external joint rate control algorithm to dynamically distribute the channel bandwidth among the program encoders such that the video quality is approximately equal in all programs. In our algorithm, the bit rate of each encoder is updated on the basis of the relative complexities of the programs measured at boundaries of groups of pictures (GOPs) and whenever scene changes are detected. The proposed algorithm requires no external preprocessing of the input video sources. Furthermore, as compared with previous work in this area, our algorithm is not restricted to operate only with encoders having the same GOP structure. Thus, the GOP boundaries at the different encoders need not be synchronized. Bit rate changes take place only at GOP boundaries, allowing the encoders to operate at a constant bit rate within GOPs. Overall, this results in a piecewise variable bit rate compression for each of the encoders. We also describe a strategy for decreasing the reaction delay of the system for scene changes. Experimental results show that the proposed multiprogram video compression system results in good picture quality with no external preprocessing, despite its relative simplicity.

A scalable chip set for MPEG2 real-time encoding

This is a description of an architecture for video compression based on the MPEG2 (MP@ML) standard. The chip set is comprised of 3 different devices. The architecture is scalable, and real-time MPEG2 systems could be built with one, two or all three chip solutions. The encoder includes an on-chip processor for programming options, and provides direct connections to external DRAM and SRAM.

Comparison of MPEG-2 and M-JPEG Video Coding at Low Bit Rates

In this paper a comparative analysis of MPEG-2 and Motion-JPEG (M-JPEG) video coding is given, and the performance of these methods is compared via experiments. At first, the algorithmic differences are discussed, then results of the experiments are shown for various video sources with different image sizes and frame rates; the bit rates ranged from 1 to 8 Mbits/sec. The results also show that MPEG-2 intraframe only (I-only) and intra- and predictive-frame (IP) encoding achieve higher picture quality at the same bit rate, or equivalent picture quality at a lower bit rate, than M-JPEG. This quantitative comparison as well as the subjective picture quality evaluation can trigger the use of MPEG-2 video coding instead of M-JPEG at low bit rates.