Complexity scalable control for H.264 motion estimation and mode decision under energy constraints

The H.264 video coding standard supports several inter-prediction coding modes using variable block sizes. The robust rate–distortion optimization (RDO) technique of both the motion estimation (ME) and the mode decision (MD) is adopted to achieve superior coding efficiency, which also entails a lot of complex computations. In this paper, by rearranging the order of candidate modes and using two new rate–distortion–complexity optimization (RDCO) functions, a more efficient RDCO framework for fast ME and MD is first proposed. Then, with this new framework, a novel complexity scalable control algorithm for H.264 inter-prediction coding is devised, which is based on an efficient complexity allocation and control (CAAC) scheme performed both at the frame level and the macroblock (MB) level. Experimental results show that our proposed algorithm can adaptively determine an appropriate cut-off point for a sequence of re-ordered candidate modes according to the current energy condition of a mobile device, which can adjust the complexity of inter-prediction coding to any appropriate level with minimum degradation in video quality. This can therefore prolong the operational lifetime of batteries.