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Buffer-constrained R-D optimized rate control for video coding is investigated in this work. A frame level bit allocation is first presented based on a model of the relationship between the rate (R) and nonzero (NZ) coefficients. With the modelled R-NZ relationship, a quality feedback scheme is proposed to generate VBV (video buffer verifier) compliant bitstream with assured video quality. Then, a R-D optimized macroblock level rate control is described by jointly selecting the quantization parameter and the coding mode of macroblocks in I, B and P pictures for both progressive and interlaced video. To avoid the irregularly large MV or one single isolated coefficient, we extend the set of coding modes of MB by including zero MV and zero texture bits as two more candidates. Finally, fast heuristics are developed to reduce the computational complexity of R-D data generation and the Viterbi algorithm (VA) in R-D optimization, which achieves coding results close to the optimal one at a much lower computational cost.