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Off-Host IDCT

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The transfer of macroblock inverse discrete-cosine transform (IDCT) coefficient data for off-host IDCT processing is done using a buffer of scan index and value information to define and specify the transform equations. Index information is sent as 16-bit words (although only 6-bit quantities are really needed for 8x8 transform blocks). Transform coefficient value information is sent as signed 16-bit words (although only 12 bits are needed for the usual case of 8x8 transform blocks and BPP equal to 8).

Transform coefficients are sent in either the DXVA_TCoefSingle structure or the DXVA_TCoef4Group structure. If the bConfig4GroupedCoefs member of the DXVA_ConfigPictureDecode structure is zero, coefficients are sent individually using DXVA_TCoefSingle structures. If bConfig4GroupedCoefs is 1, coefficients are sent in groups of four using DXVA_TCoef4Group structures.