Fast mode decision for H.264

H.264 can be coded with 7 different block sizes for motion-compensation in the inter mode, and various spatial directional prediction modes in the intra mode. To achieve as high a coding efficiency as possible, the H.264 encoder employs a complex mode decision technique based on rate-distortion optimization. It calculates rate distortion cost (RDcost) of all possible modes to choose the best one having the minimum RDcost. Therefore, this mode selection method calls for high computational complexity. In order to reduce the complexity, we propose two techniques - 'early SKIP mode decision' and 'selective intra mode decision'. The simulation results show that without considerable performance degradation, the proposed methods reduce encoding time by 30% on average and save the number of computing rate-distortion costs by 72%.