Dirac uses macroblock structures to introduce a degree of adaption into motion estimation by allowing the size of the blocks used to vary. The motion estimation stage of the encoding is organised by macroblock, and each combination of block size and prediction mode is tried using the RDO block-matching metric - this is called mode decision in the software - and the best solution adopted macroblock by macroblock.
Macroblocks and variable-sized block matching
Block data
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