Content-Adaptive Rate-Distortion Modeling for Frame-Level Rate Control in Versatile Video Coding
Junqi Liao, Li Li, Dong Liu, Houqiang Li
Abstract
Rate control (RC) plays an essential role in video coding. RC algorithms based on more accurate rate-distortion (R-D) models often achieve higher control precision and better R-D performance. The most widely used R-D model for HEVC and VVC is the hyperbolic R-D model, which is equivalent to a linear relationship between <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ln {R}$</tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\ln {D}$</tex-math></inline-formula> . Due to its high accuracy, few studies have attempted to improve the accuracy of the hyperbolic R-D model further. Intuitively, we consider that the accuracy of the hyperbolic R-D model could be further improved by increasing the order of the R-D model. However, this may also increase the number of model parameters to be estimated, which may not benefit the one-pass RC precision. In this paper, we first explicitly note that there is a trade-off between the order of the R-D model and the difficulty in estimating the model parameters in one-pass RC. Then, motivated by the trade-off, we propose high-order R-D models and the corresponding one-pass frame-level RC algorithms for video coding. Finally, we introduce the quadratic R-D model into frame-level RC in the VVC Test Model (VTM-19.2) and provide a content-adaptive model selection between the first-order and second-order R-D models. Experimental results show that the proposed frame-level RC algorithm based on the quadratic R-D model reduces the average frame-level bitrate error by 5.30%, 3.11%, and 13.45% and achieves 0.49%, 0.65%, and 0.35% BD-Rate savings under Low Delay B (LDB), Low Delay P (LDP), and Random Access (RA) configurations, respectively, when compared to the default RC algorithm used in VTM-19.2.