This paper proposes a fast algorithm that converts DCT coefficients into integer transform coefficients, for the transform domain transcoding from MPEG-x to H.264. For the transcoding in the same resolution, the 8 /spl times/ 8 DCT coefficients are converted to four 4/spl times/ 4 integer transform coefficients by decomposing the conversion matrix into sparse ones. For the reduction of resolution by half, we also propose an algorithm that converts DCT coefficients in the lower band into 4 /spl times/ 4 integer transform coefficients. The sparse matrices derived in this paper require fewer computations than the direct and conventional conversion matrices, and thus the overall transcoding using the proposed algorithm requires less computational complexity.