The H.264/AVC video encoder standard significantly improves the compression efficiency by using variable block-sized Inter (P) and Intra (I) Macroblock (MB) coding modes. In this paper, we propose a novel Human Visual System based Adaptive Computational Complexity Reduction Scheme (ACCoReS). It performs Prognostic Early Mode Exclusion and a Hierarchical Fast Mode Prediction to exclude as many I-MB and P-MB coding modes as possible (up to 73%) even before the actual Rate Distortion Optimized Mode Decision (RDO-MD) and Motion Estimation while keeping a good quality. In the best case, ACCoReS processes exactly one MB Type and one corresponding nearoptimal coding mode, such that the complete RDO-MD process is skipped. Experimental results show that compared to state-of the-art approaches (, -), ACCoReS achieves a speedup of up to 9.14x (average 3x) with an average PSNR loss of 0.66 dB. Compared to exhaustive RDO-MD, our ACCoReS provides a performance improvement of up to 19x (average 10x) for an average 3% PSNR loss.