1. A computer-readable storage device storing computer-executable instructions that, when executed, cause one or more processors to perform acts comprising: establishing a lookup table that includes entries used for combined coding of an inter-prediction direction and one or more corresponding frame index values for an inter-prediction of pixel data of a coding unit in a frame; providing an additional entry to the lookup table that indicates that a corresponding number of index values in at least one group of frames exceeds a predetermined value; and implementing a maximum index value for the lookup table based at least on a number of frames in each group of frames used in the inter-prediction of pixel data for the coding unit.