Efficient coding unit size selection for HEVC downsizing transcoding

This paper presents an efficient method to speed up High Efficiency Video Coding (HEVC) downsizing transcoding. Specifically, we focus on the coding unit (CU) size selection, one of the most computationally intensive processes in HEVC, to reduce the complexity of the transcoder. The proposed method utilizes the temporal correlation of depth levels among CUs and the continuity of the motion vector field in the precoded video to derive the most probable CU depth ranges and avoid the unnecessary exhaustive CU size search at certain depth levels. Experimental results show the proposed method can reduce the overall transcoding time by about 41% on average while maintaining the similar performance to that obtained by the cascaded re-encoding transcoder.