engleski

Video Quality Improvement by Variable Bit Rate Coding

In this paper, the subjective performance of video sequences coded with variable and constant bit rate using MPEG-1 video coding standard, will be examined. Variable bit rate video coding makes it possible to deliver video of constant quality by alternating the bit rate of the compressed signal according to the content of the video input. Contrary, the ultimate goal of current constant bit rate coding schemes is to maximize quality of video signal at a given bit rate. With these points in mind, we will focus our discussion on question "what improvement in picture quality can be achieved by replacing constant with variable bit rate coding". To analyze the improvement in quality that can be expected from variable bit rate coding, the subjective testing of picture quality were conducted on three different types of video sequences in terms of scene content, complexity and motion. The selected sequences were coded using MPEG-1 compression techniques with variable and constant bit rate. The variable bit rate coding was controlled by controlling quantizer scale factor to keep the quality at constant value. For an identical input video sequence, the value of constant bit rate is chosen to be close to the average value of variable bit rate. Formal subjective assessment was performed by non-experts viewers on the test sequences coded at constant and variable bit rates. For the sequences coded at variable bit rates and different quality levels, statistical parameters such as bit rate distributions, peak bit rate and average bit rate are given. Based on results of subjective testing, the comparison of variable and constant bit rate coding quality has been made and subjective quality improvement obtained by variable bit rate coding has been discussed.

video compression; constant bit rate coding; variable bit rate coding; picture quality; quantizer scale factor; compression ratio

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