Research On Transcoding From H.264/AVC To HEVC

With the rapid development of multimedia technology and the wide application of high-definition video, higher compression ratio and better video reconstruction quality have become the main objectives of video codec technology. In this context, the JCT-VC established by the Moving Picture Experts Group and the Video Coding Experts Group developed a new video coding standard HEVC after years of effort. Compared with the previous video coding standard H.264/AVC, HEVC can reduce 50% bit rate with the same reconstruction quality. The promotion and development of HEVC standard become a necessity.Due to many video encoding equipments and transmission mode also uses H.264/AVC standard, HEVC standard is difficult to completely replace previous standard, and two standards will coexist for a long time. H.264/AVC to HEVC video transcoding has become a meaningful research. The introduction of more detailed block division methods and more complex coding methods make coding complexity of HEVC standard several times higher than H.264/AVC. Based on this, the paper studies how to use the coding information from H.264/AVC standard to judge HEVC encoding process in advance, thereby to reduce the complexity of HEVC and improve transcoding efficiency.In this paper, correlation analysis of coding information including prediction modes, DCT quantized coefficients and motion vectors from H264/AVC standard and HEVC standard is studied at first. A lot of statistical experiments are done for these three types of information. Based on the experiment results, a transcoding method from H.264/AVC to HEVC based on combination of SKIP macroblock and motion vector is proposed. This method utilizes SKIP macroblock and motion vector information from H.264/AVC encoding process to determine smooth level of each frame, and then determine the degree of decomposition and prediction mode of each LCU in HEVC encoding process, thereby to reduce coding complexity.A controllable complexity transcoding method from H.264/AVC to HEVC based on combination of DCT quantized coefficient and motion vector is also proposed. This method utilizes DCT quantized coefficient and motion vector information from H.264/AVC encoding process to determine the degree of decomposition and prediction mode of each LCU in HEVC encoding process.The threshold of motion vector variance can be adjusted to meet different rate-distortion performance and complexity requirements. This greatly improves the flexibility of the transcoding method.