Video coding device and video transmission system using the same, quantization control method and average throughput calculation method used therein

摘要

The invention relates to a video coding device in which operating points is predetermined as a balance between timewise distortion due to frame dropping according to a coding rate, which is a rate of frames transmittable per unit time, and spatial distortion due to a quantization step size when low bit rate compression coding a moving picture and transmitting the coded video data through a communication line with a low bit rate, the device comprising video input means for forming a video frame from a picture signal and outputting the video frame; coding means for coding the video frame formed in said video input means; a transmission buffer for storing the video data coded in said coding means; quantization control means for determining a quantization step size corresponding to communication conditions, and transmission control means for transmitting the video data in said transmission buffer at a certain transmission rate, wherein said quantization control means calculates an average throughput in a predetermined constant period of time, calculates the coding rate on the basis of the calculated average throughput and the amount of generated information per one frame resulting from coding in said coding means, and determines a quantization step size most suitable in view of visual properties corresponding to the calculated coding rate and sends the quantization step size to said coding means, and sends said coding portion a notice to code one video frame when the remaining amount of data in said transmission buffer falls below a predetermined threshold.