In a first exemplary media implementation, one or more processor-accessible media include processor-executable instructions that, when executed, direct a device to perform actions including: comparing an accuracy indicator to at least one threshold, the accuracy indicator corresponding to a reference macroblock selected for a target macroblock; ascertaining a refinement case from multiple refinement cases based on the comparing, each refinement case of the multiple refinement cases defining multiple test points in relation to the reference macroblock; and analyzing the ascertained refinement case with regard to the target macroblock. In a second exemplary media implementation, one or more media include processor-executable instructions that, when executed, direct a device to perform actions including: determining if two chrominance sums have magnitudes that are each less than a first product and four luminance sums have magnitudes that are each less than a second product; and if so, forwarding all zero values for a macroblock.