1. A method comprising: deriving a coding mode indicator specifying a partition of enhancement layer block based at least in part on a plurality of reference frame index values corresponding to a plurality of reference layer blocks, the reference layer blocks representing an area in a base layer that, after upsampling, covers the enhancement layer block, wherein the partition's size is determined by merging reference layer blocks that have the same reference frame index and that have motion vectors having a difference metric less than a predetermined threshold, wherein the difference metric is derived by a sum of absolute difference of motion vector components; deriving a motion vector associated with the partition of the enhancement layer block, wherein the derived motion vector comprises a weighted average of the motion vectors of the merged reference layer blocks before merging, wherein weights for the weighted average are based on differentials between the motion vectors of the reference layer blocks before merging, partition sizes associated with the reference layer blocks before merging, or a macroblock type or mode associated with the reference layer blocks before merging; and encoding the enhancement layer block utilizing the coding mode indicator and the derived motion vector; wherein the predetermined threshold is equal to one.