The work carried out by the authors on heterogeneous video transcoding (see Shanableh, T. and Ghanbari, M., IEEE Trans. on Multimedia, vol.2, no.2, p.101-10, 2000) is extended to the DCT domain. The heterogeneous video transcoder was mainly proposed for achieving portability between different encoding formats, namely, from MPEG-1/2 into H.261/3 with lower spatio-temporal resolutions. The motion compensation (MC) loops of the decoder-encoder cascade are now simplified by eliminating the DCT/IDCT pairs whilst performing picture decimation and MC in the DCT domain (MC-DCT). Two transcoding architectures are proposed, in one, both the MC-loops are in the DCT-domain, while in the other, it is shown that by implementing the encoder's MC-loop in the pixel domain higher flexibility and better results are achieved. Methods for accelerating the MC-DCT are then divided into two broad categories of lossless and lossy methods. It is shown that by utilising shared information among successive motion compensated macroblocks, better results over those reported in the literature are achieved.
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