The new video coding standard, High Efficiency Video Coding (HEVC), has been established to succeed the widely used H.264/AVC standard. However, an enormous amount of legacy content is encoded with H.264/AVC. This makes high performance AVC to HEVC transcoding in great need. This paper presents a fast transcoding algorithm based on residual and motion information extracted from H.264 decoder. By exploiting these side information, regions' homogeneity characteristic are analysed. An efficient coding unit (CU) and prediction unit (PU) mode decision strategy is proposed combing regions' prediction homogeneity and current encoding information. The experimental results show that the proposed transcoding scheme can save up to 55% of encoding time with negligible loss of coding efficiency, when compared to that of the full decoding and full encoding transcoder.Index Terms-HEVC, transcoding, fast partition decision, residual homogeneity, motion homogeneity.
I. INTRODUCTIONH.264/AVC video coding standard has achieved great success and been widely used for video streaming and storage. Meanwhile, HEVC standard was standardized in 2013 to meet the growing demands for ultra-high-definition videos applications [1]. With more than 50% of encoding gains, HEVC is expected to be the successor to H.264/AVC in the near future. The demand for transcoding is rising, since large amount of content encoded in H.264 can achieve better ratedistortion performance by converting to HEVC format.The H.264 to HEVC format transcoding is heterogeneous transcoding, which mainly changes the bitstream format and reduces the bitrate. Trivial solution is achieved by completely decoding the source stream, and then completely re-encoding it in the target format. This full decoding and full encoding (FDFE) method can maximum the Rate-Distortion performance, but not efficiency in terms of computational complexity. This is the main problem faced by practical H.264/AVC to HEVC transcoding service.For transcoding, HEVC encoder is still using the blockbased hybrid coding framework, which is similar to H.264/AVC. Many encoding sections are sharing similar techniques, such as motion estimation, transform, quantization, and entropy coding. It makes the fast H.264/AVC to HEVC transcoding meaningful and possible. For the transcoder, much information can be extracted from H.264/AVC decoder to reduce HEVC encoding complexity and improve efficiency. There are many features in the source bitstream which can be used, such as motion vector (MV), mode information,
