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Parameters other than the MB splitting level are termed block data, even though they may apply to blocks, sub-MBs or the MB itself depending on the value of the splitting mode. The prediction mode has already been described. The five remaining block parameters are:

REF1_x: horizontal component of motion vector to the first reference frame;

REF1_y: vertical component of motion vector to the first reference frame;

REF2_x: horizontal component of motion vector to the second reference frame;

REF2_y: vertical component of motion vector to the second reference frame.

DC: DC or average value for the prediction unit for each component (Y, U or V) being coded, to 8-bit accuracy.

Clearly not all of these values must be coded. If the prediction mdoe is REF1_ONLY then REF2_x and REF2_y will not be coded, for example, and if the prediction unit is not INTRA, then no DC value need be sent.

Each different type of block data is coded as a separate block of data, allowing for parallelisation of the decoding process.

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