Transcoding H.265/HEVC

Abstract: Video transcoding is the process of converting compressed video signals to adapt video characteristics such as video bit rate, video resolution, or video codec, so as to meet the specifications of communication channels and endpoint devices. A straightforward transcoding solution is to fully decode and encode the video. However this method is computationally expensive and thus unsuitable in applications with tight resource constraints such as in software-based real-time environment. Therefore, efficient transcoding meth- ods are required to reduce the transcoding complexity while preserving video quality. Prior transcoding methods are suitable for video coding standards such as H.264/AVC and MPEG-2. H.265/HEVC has introduced new coding concepts, e.g., the quad-tree-based block structure, that are fundamentally different from those in prior standards. These concepts require existing transcoding methods to be adapted and novel solutions to be developed. This work primarily addressed the issue of efficient HEVC transcoding for bit rate adaptation (reduction). The goal is to understand the transcoding behaviour for some straightforward transcoding strategies, and to subsequently optimize the complexity/quality trade-off by providing heuristics to reduce the number of coding options to evaluate. A transcoder prototype is developed based on the HEVC reference software HM-8.2. The proposed transcoder reduces the transcoding time compared to full decoding and encoding by at least 80% while inducing a coding performance drop within a margin for 5%. The thesis has been carried out in collaboration with Ericsson Research in Stockholm