A Fast Scheme for Converting DCT Coefficients to H.264/AVC Integer Transform Coefficients

Converting MPEG-2 8-tap discrete cosine transform (DCT) coefficients to H.264/AVC 4-tap integer transform (IT) coefficients is one of the indispensable operations for MPEG-2 to H.264 transform domain transcoding. In this paper, we propose a novel transform kernel matrix based on the factorization of DCT to perform this operation directly in transform domain. Furthermore, additional reduction in computation can be obtained by taking advantage of the fact that most of the 8×8 DCT blocks in real video sequences only have nonzero coefficients in the upper left 4×4 quadrant. Relative to Jun Xin’s method, the proposed method saves 16 operations in the worst case and 440 operations in the best case for each 8×8 DCT block. Experimental results also show that the proposed method efficiently reduces the computational cost up to 42.9% with negligible degradation in video quality. Hence, the proposed method can be efficiently used in the real-time and high capacity MPEG-2 to H.264 transform domain transcoding.