Edward F. Westermann

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.

MAXIMIZING AND MAINTAINING AC TEST ACCURACY IN THE MANUFACTURING ENVIRONMENT

The need for sub-nanosecond (ns) test accuracy is especially acute in array testing, where margins of only a few hundred picoseconds (ps) may exist. The challenge of maximizing tester accuracy is increased when the tester must perform in a manufacturing environment, where capacity is as important as accuracy. This, at least partially, explains why some form of autocalibration is standard on virtually all modcrn test equipment. In spite of autocalibration, achieving accurate AC test iesults ui a volume manufacturing environment remains an elusive goal.