Abstract: Rate-Distortion Optimization (RDO) technique is employed in AVS (Audio Video Coding Standard) to improve coding efficiency．However,the computational complexity increases drastically since the encoder has to encode the microblock by measuring RD costs of all the possible modes,which makes it difficult to meet the demands of real-time encoding．After the theory of the intra prediction and the process of the intra mode decision were analyzed,the fast intra prediction algorithm based on SATD (Sum of Absolute Transformed Differences) criterion and spatial correlation was proposed to optimize intra mode decision and reduce the complexity．First,some candidate modes were selected based on block’s SATD which decreases the number of intra prediction mode．Then,mode correlation of neighbor blocks was used to reduce the complexity of luminance blocks and improve the speed of mode decision．Experimental results indicate that encoding time of the proposed approach is averagely reduced by 53.56% than that of AVS standard algorithm with similar encoding efficiency．Compared with the classical algorithm based on edge detection,the encoding time is saved by 16.39% on average while keeping better image quality and lower bite-rate．

Key words: AVS,Intra prediction,Mode decision,SATD,RDO