Studying rate control methods for UHDTV delivery using HEVC

Since the early video coding standardisation efforts, rate control has been considered essential for almost any application. With the advent of improved video coding standards and the introduction of advanced flexible coding tools, previous Rate-Distortion (RD) models used for rate control have become obsolete. To address this issue, some rate control methods have been recently proposed specifically for the current state-of-the-art High Efficiency Video Coding (HEVC) standard which introduce many useful features, such as a robust correspondence between the rate and Lagrange multiplier λ. However, when applying these rate control methods on sequences in the new Ultra High Definition Television (UHDTV) format, degraded coding performance was observed. In this paper, an analysis of the state-of-the-art HEVC rate control method was performed and two directions for its improvement were evaluated. These improvements target frame-level bit-allocation and model parameter initialisation. When compared to the rate control method implemented in the HEVC reference software, these improvements result in reduced BD-rate losses of 3.1% and 2.1%, versus the 8.8% provided by the reference algorithm. Moreover, the proposed improvements increase the accuracy in hitting the target bit-rate.