Adaptive fast block mode decision algorithm for H.264/AVC

H.264/AVC outperforms the previous coding standards thanks to variable block size motion compensation (VBSMC) ranging from 4 × 4 to 16 × 16 in interframe coding. However, this new feature causes extremely high computation complexity when rate-distortion optimization(RDO) is performed using full mode decision. In this paper, we propose an adaptive fast block mode decision algorithm (AFBMD) leveraging the following characteristics to significantly reduce the complexity. (1) detecting stationarity of a block by using sum of absolute difference (SAD) and the biggest pixel difference. (2) exploiting the left and upper block modes to determine the block mode priority order. (3) comparing the RDcosts of the current best block mode and the block modes in the priority order that attempt to early terminate the block mode decision. Compared with the full mode decision (FMD) [20], the experimental results shown that the proposed algorithm reduces the mode decision complexity up to 77% while still maintains almost the same image quality as FMD.