Study of an efficient transmission technique for motion-image media based on an optimal-frame-rate estimation

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Since the bit rate of a motion image is a product of the average amount of bits per second(BPF) and the number of frames per second(FPS), these two values are inversely proportional to each other under a bit rate constraint. Therefore, a proper selection of the FPS and BPF is necessary in a efficient transmission of a target motion image with a limited bandwidth. The head investigator of this research has considered this problem and has proposed a fundamental technique for estimating the optimal FPS for a target image sequence which maximizes the subjective quality of the target sequences under a fixed transmission bit rate. The objective of this research is to develop a detailed algorithm for applying the technique to an actual motion image, and to implement it as an actual motion image encoder (transcoder).We have first developed an algorithm for applying the optimal-frame-rate estimation technique to actual long motion images which consist of numbers of "scenes" having time-varying motion and frame activities. We have also considered a rate control algorithm for a constant-bit-rate encoding to develop a detailed procedure for controlling the rate for time-varying FPSs.Finally, we have implemented the developed algorithms in an MPEG4 encoder to realize a MPEG4-based transcoder, which convert an incoming MPEG4 bit stream to one with a given lower bit rate. Comparisons with a fixed FPS approach have confirmed the effectiveness of the proposed approach.