A fast MPEG-4 to H.264/AVC intra frame transcoding algorithm

This paper presents an intra-frame coding mode decision algorithm for MPEG-4 to H.264/AVC transcoding in integer transform domain. The edge direction inside a block is estimated in the integer transform domain to reduce candidate prediction modes. Based on the analysis of the variance of the sixteen subblock DC coefficients inside a macroblock, “transition interval” and “double thresholds” intra prediction size selection are proposed to reduce wrong judgments. According to statistical results of high probability of neighboring blocks having the same intra prediction mode, a decision rule is given to predict the coding mode of the current block from its neighbors. The proposed transcoding algorithm can reduce computation time by more than 75% comparing with the pixel domain cascaded intra-frame transcoder, while maintains similar picture quality and bitrate.