Optimal Bitrate Allocation in the Scalable HEVC Extension for the Deployment of UHD Services

Ultra high definition (UHD) is the latest trend in broadcasting area, which enables new services with 3840×2160 resolution and comes with enhanced color-gamut, frame-rate, dynamic range, and better audio system compared to the currently deployed HD services. The UHD format for broadcasting is already under standardization in the digital video broadcasting consortium which plans to introduce UHD services in three phases. The increase in data brought by these services requires more efficient compression and transmission systems. The recent scalable video coding standard scalable High Efficiency Video Coding (SHVC) is a promising candidate to handle these three phases while ensuring backward compatibility. Moreover, delivering such contents over networks needs an accurate control of the output bitrate from encoder engines to match rigid constraints on bandwidth and QoS. Several contributions have already been proposed to jointly encode scalable stream, but without considering the impact of bitrate ratio between layers on the compression performance. In this paper, the impact of the bitrate ratio between layers on the coding performance is first investigated for several UHD scalable schemes including spatial, color-gamut, and SDR-to-HDR scalability in SHVC. Based on this investigation, an adaptive rate control algorithm which dynamically allocates the bitrate between two layers is proposed to optimize the performance under quality and bitrate constraints. The algorithm has been implemented in the SHVC reference software (SHM9.0) and tested over 15 video sequences under two industrial usecases. The performance shows an average BD-BR improvement of 7.51% and 3.35% for these two use-cases.