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

由于运动图像的比特率是每秒平均比特量(BPF)和每秒帧数(FPS)的乘积，因此在比特率约束下，这两个值彼此成反比。因此，在有限带宽的目标运动图像的有效传输中，FPS和BPF的适当选择是必要的。这项研究的带头人考虑了这个问题，并提出了一种基本的方法来估计目标图像序列的最优FPS，在固定的传输比特率下最大化目标序列的主观质量。这项研究的目的是开发一种将该技术应用于实际运动图像的详细算法，并将其实现为实际的运动图像编码器(代码转换器)。我们首次开发了一种将最优帧速率估计技术应用于实际的长运动图像的算法，该算法由多个具有时变运动和帧活动的场景组成。最后，我们在MPEG4编码器中实现了一个基于MPEG4的转码器，将输入的MPEG4码流转换成具有给定较低比特率的码流。与固定FPS方法的比较证实了该方法的有效性。

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.