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数（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，为了在有限带宽下有效传输目标运动图像，正确选择帧速率和帧速率是必要的。本研究的首席研究员已经考虑到这个问题，并提出了一种基本技术来估计目标图像序列的最佳FPS，该技术在固定传输比特率下最大化目标序列的主观质量。本研究的目的是开发一种详细的算法，将该技术应用于实际的运动图像，并将其实现为实际的运动图像编码器（转码器）。我们首先开发了一种算法，用于将最佳帧率估计技术应用于实际的长运动图像，这些图像由具有时变运动和帧活动的“场景”组成。我们还考虑了一种用于恒定比特率编码的速率控制算法，以开发一种用于控制时变fps速率的详细程序。最后，我们在MPEG4编码器中实现了所开发的算法，以实现基于MPEG4的转码器，该转码器将传入的MPEG4比特流转换为具有给定较低比特率的比特流。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.