Fast intra mode decision algorithm for H.263 to H.264/AVC transcoding

In this paper, we present a fast mode decision method for H.263 to H.264/AVC intraframe transcoding. The proposed algorithm is based on the observation that features of DCT coefficients extracted from H.263 coded intraframe strongly relates to the optimal mode in H.264/AVC intra mode decision. Specifically, the total number of non-zero AC coefficients of four 8times8 DCT blocks in H.263 is taken as a measurement in the intra block size decision. The objective is to reject improbable block types in earlier stages in order to achieve computation saving. In addition, a transform domain edge direction estimation is also adopted into our scheme to further speed up the intra mode prediction. Simulation results show that the proposed approach can reduce the computational complexity of intraframe transcoding by up to 65% while maintaining the rate-distortion (R-D) performance.