Studying rate control methods for UHDTV delivery using HEVC

Abstract

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 framelevel bit-allocation and model parameter initialisation. When compared to the rate control method implemented in the HEVC reference software, these improvements result in reduced BDrate 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.

Two-pass rate control for UHDTV delivery with HEVC

“…As demonstrated in our previous work [20], initialising the Rλ model parameters on a per sequence and QP basis leads to improved coding performance of the rate control method. However, in practical applications, it is not feasible to encode a sequence with multiple different QP values in order to fit the R-λ model.…”

“…This results in high QP values used after the shot change, as shown in Figure 1. In our previous study on rate control in HEVC [20], an analysis was carried out which proved that the encoding efficiency can be improved with the new frame-level rate allocation obtained from pre-encoding and model parameter initialisation after fitting the data from pre-encoding.…”

Two-Pass Rate Control for Improved Quality of Experience in UHDTV Delivery

“…Finally, the QP value is 381 determined as: This section presents the proposed two-pass rate control 414 method for compression of UHDTV video content. Besides describing the proposed method, it is also interesting to analyze the current limitations for the state-of-the-art HEVC rate control method as well as the theoretical performance that can be achieved in case of unlimited computational resources [33], i.e. when the encoder can perform the pre-encoding step testing all possible coding modes to derive the actual bit-rate profile, which is then used in the real encoding step.…”