The Research Of Multi-rate Video Transcoding Technologies Based On HEVC

The High Efficiency Video Coding(HEVC)has achieved 50% bitrate reduction under the same video quality,when compared with its predecessor H.264/AVC.But the increase of coding complexity limits its practicabitity.In internet video application,in order to match different network bandwidth environment of different users,the same video usually need to be encoded several times to produce different bitrate streams.Multiple coding makes coding complexity much higher.Therefore,the research of multi-rate video transcoding thechnologies based on HEVC is urgent and important.This paper utilize a multi-rate transcoding system with one master encoder and several slave encoders.All these encoders are based on x265 encoder.This paper completes the optimization of multi-rate system in two aspects,one is the optimization of simgle x265 encoder,the other is the optimization of slave encoders using coding information of master encoder.For the optimization of single x265 encoder,this paper proposed two fast inter mode decision algorithms.One is based on the reduction of CU search range,the other is based on the reduction of Rate-Distortion Optimazation(RDO)time,these two algorithms can save 13% and 19% the whole coding time separately.Moreover,this paper designs an efficient SAO coding algorithm to early terminate SAO process based on inter 64x64 skip mode,CTU spatial-domain correlations,and relations between luma and chroma.Experimental results show that the proposed algorithm can save 72.2% SAO processing time with only 0.52% BDBR increase which is negligible.For the transcoding optimization of slave encoders,this paper proposed three fast algorithms,namely,CU depth range information reuse algorithm,inter prediction mode information reuse algorithm and reference frame information reuse algorithm.The final multi-rate transcoding system can save 70% whole encoding time with only 4.7% BDBR increase or 0.105 dB BDPSNR loss which is negligible.