An Improved Parametric Bit Rate Model for Frame-Level Rate Control in Video Coding

In a hybrid video encoder, the DCT transform or integer transform are adopted to de correlate the residual correlation among neighboring pixels. However, different transform coefficients have very different variances. For example, in a 4x4 integer transform, the 16 coefficients show a decreasing variance in the well-known zigzag scan order as used in H.264. As a result, the coefficients of higher frequency have higher probability of being zeroes after quantization. On the other hand, the coefficients of lower frequency have larger variances after quantization. Such characteristics are exploited by the run-level mapping after zigzag scan to further increase the coding efficiency of entropy coding.