SNR-Based Frame-Level Video Bit Rate Allocation

Quality fluctuation has a major negative effect on perceptive video quality. In [1], we derived accurate approximations in close-form for the highly nonlinear rate-distortion (R-D) and distortion-quantization (D-Q) relationships, all at the frame-level. Based on the two close forms, we can allocate the bit rate at the frame-level rather easily as far as a target distortion for each frame could be established. In [1], a target distortion was set up for each frame based on a hypothesis that maintaining constant distortion over frames would boast video quality smoothing and extensive experiments showed the constant-distortion bit allocation (CDBA) scheme significantly outperformed the popular constant bit allocation (CBA) scheme in terms of delivered video quality. Maintaining constant distortion is no different from maintaining constant Peak-signal-to-Noise-Ratio (PSNR). In scene changes, however, the picture energy often dramatically changes, producing significantly different Signal-to-Noise-Ratio (SNR) if constant distortion or constant PSNR is maintained. Although computationally more complex, SNR represents a more objective measure than PSNR in assessing picture/video quality. In the paper, an SNR-based bit allocation scheme is developed for video quality smoothing. The algorithm uses a single pass and attempts to maintain constant SNR at the frame level throughout the video sequence. Experimental results on all testing video sequences show that the proposed CSNRBA scheme provides smooth video quality in terms of natural color and sharp objects and silhouette significantly better than both the CBA and CDBA schemes.