Fast Inter Mode Decision Algorithm Based on Mode Mapping and Decision Tree for P Frames in MPEG-2 to H.264/AVC Transcoding

摘要

There is an inevitable requirement of transcoding from MPEG-2 to H.264/AVC in many video applications. Due to the use of variable block sizes and rate-distortion optimization techniques in H.264, there is extremely high computational complexity in the reference cascaded transcoder. To reduce the complexity, this paper presents a fast inter mode decision algorithm for P frames in MPEG-2 to H.264/AVC transcoding. Firstly, with the statistical analysis of the correlation between the MB's coding mode in MPEG-2 and the corresponding mode in H.264/AVC, the proposed algorithm directly determines the candidate modes for some special MBs based on the mode mapping rules. Then for other MBs, machine learning tools are used to exploit the correlation between the residual MB information in MPEG-2 and the coding mode in H.264/AVC, and the decision tree is derived to determine the candidate modes. The proposed algorithm efficiently reduces the number of candidate modes in H.264/AVC encoder. Experimental results show that the proposed algorithm can achieve 60 % of transcoding time saving on average with the less PSNR degradation and bitrate increase, comparing with the reference cascaded transcoder.