Process for the format conversion of MPEG bitstreams, a system and computer program product therefor

A process for format conversion of DCT macroblocks in an MPEG video bitstream that are divided into blocks, each of which includes a plurality of microblocks. In each DCT block, the significant frequencies are identified and preserved, isolating a corresponding microblock preferably consisting of the microblock on the top left of each block and setting to zero the coefficients of the remaining microblocks. On the microblock thus isolated there is performed an inverse discrete cosine transform, and the microblock thus obtained is merged with the homologous microblocks obtained from the other blocks comprised in a respective starting macroblock, so as to give rise to a merging block. The merging block thus obtained undergoes a discrete cosine transform so as to obtain a final block, which can be assembled into a macroblock with converted format.