Frame-level Complexity Control in H.264 Video Coding

H.264 video coding standard supports several interprediction coding modes that use macroblock partitions with variable block sizes. Unfortunately, searching for optimal motion vectors of each possible partition incurs a heavy computational cost. In this paper, we propose a novel frame-level complexity control algorithm that determines for each macroblock which partitions are likely to be optimal. Motion vector search is carried out for only the selected partitions, thus reducing the complexity of the motion estimation step. The mode selection criteria is based on a measure of spatio-temporal activity within the macroblock. For each frame, the procedure guarantees that an execution time budget is met with minimum loss of coding efficiency. Simulation results show that the algorithm speeds up integerpel motion estimation by a factor of up to 40 with less than 0.2 dB loss in coding efficiency.