A Generalized Rate-Distortion-$λ$ Model Based HEVC Rate Control Algorithm
This work addresses the need for more efficient video compression in practical applications like streaming and broadcasting, representing an incremental improvement over prior rate control algorithms.
The paper tackles the problem of improving rate control accuracy and video quality in HEVC/H.265 encoding by proposing a novel generalized rate-distortion-λ model, achieving average BDBR savings of 6.09%, 3.15%, and 4.03% across different configurations compared to existing methods.
The High Efficiency Video Coding (HEVC/H.265) standard doubles the compression efficiency of the widely used H.264/AVC standard. For practical applications, rate control (RC) algorithms for HEVC need to be developed. Based on the R-Q, R-$ρ$ or R-$λ$ models, rate control algorithms aim at encoding a video clip/segment to a target bit rate accurately with high video quality after compression. Among the various models used by HEVC rate control algorithms, the R-$λ$ model performs the best in both coding efficiency and rate control accuracy. However, compared with encoding with a fixed quantization parameter (QP), even the best rate control algorithm [1] still under-performs when comparing the video quality achieved at identical average bit rates. In this paper, we propose a novel generalized rate-distortion-$λ$ (R-D-$λ$) model for the relationship between rate (R), distortion (D) and the Lagrangian multiplier ($λ$) in rate-distortion (RD) optimized encoding. In addition to the well designed hierarchical initialization and coefficient update scheme, a new model based rate allocation scheme composed of amortization, smooth window and consistency control is proposed for a better rate allocation. Experimental results implementing the proposed algorithm in the HEVC reference software HM-16.9 show that the proposed rate control algorithm is able to achieve an average of BDBR saving of 6.09%, 3.15% and 4.03% for random access (RA), low delay P (LDP) and low delay B (LDB) configurations respectively as compared with the R-$λ$ model based RC algorithm [1] implemented in HM. The proposed algorithm also outperforms the state-of-the-art algorithms, while rate control accuracy and encoding speed are hardly impacted.