Quantization parameter (QP) cascaded hierarchical prediction structures have been proved as efficient techniques in hybrid video coding. However, the current QP cascading method is empirical and not adaptive. The reason for the higher coding efficiency of this method has not been fully explored so far. In this paper, the rate-distortion performance of QP cascaded hierarchical video coding is first analyzed with dependent rate-distortion function. Then the optimal offset in linear QP cascading scheme is derived theoretically. It is shown that the widely accepted empirical QP cascading method is actually an approximation to the theoretical solution in fast movement environment. For slow sequences, an average gain of 0.43 dB can be achieved by the combination of two proposed adaptive algorithms.
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