Adaptive fast DIRECT mode decision algorithm using mode and Lagrangian cost prediction for B frame in H.264/AVC

In this paper, a fast spatial DIRECT mode decision method for B frame in H.264/AVC is proposed. It is based on a statistical analysis on multiple video sequences, and the strong relationship of mode selection and rate-distortion (RD) cost between the current DIRECT macroblock (MB) and the co-located MBs is observed. With the check of mode condition and adaptive threshold of RD cost, the complex mode decision process can be released at an early stage even for small QP cases. Simulation results demonstrate the proposed method can achieve much better performance than the original exhaustive rate-distortion optimization (RDO) based mode decision algorithm by reducing up to 57.1 % of motion estimation (ME) time for IBPBP picture group with only negligible bit increment and quality degradation.