Estimation of Optimal Layer-Level Bit Allocation in Multilayer Coding

The latest video coding standard, Versatile Video Coding (VVC), supports multilayer coding and has been actively studied to deliver a variety of videos, such as multi-resolution (2K and 4K) videos, efficiently. To evaluate the compression performance of multilayer coding, a rate-distortion optimization theory-based framework was recently proposed. Using this framework, the optimal bitrate allocation (OBA) between the base layer (BL) and enhancement layer (EL) can be derived. The OBA is defined as the combination of BL and EL bitrates that maximizes the sum of Peak Signal-to-Noise Ratio (PSNR) values of low-resolution (2K) and high-resoltion (4K) videos. However, the PSNR does not always correlate with subjective quality. Moreover, the OBA varies depending on the video content features, indicating the need to estimate the OBA individually using a method that is tailored to the features. Therefore, we investigated the OBA using the Video Multimethod Assessment Fusion (VMAF) as a video quality metric and then developed a method to estimate the video-adaptive OBA. In this study, the OBA was derived analytically based on the rate-distortion curves obtained from multilayer coding experiments, and the proposed method estimated the OBA using video features as parameters. The proposed method could estimate the OBA with high correlations and small errors, with a Pearson linear correlation coefficient of 0.94, Spearman rank order correlation coefficient of 0.90, and root mean square error of 0.04.