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The High Efficiency Video Coding (HEVC/H.265) standard doubles thecompression efficiency of the widely used H.264/AVC standard. For practicalapplications, rate control (RC) algorithms for HEVC need to be developed. Basedon the R-Q, R-${\rho}$ or R-${\lambda}$ models, rate control algorithms aim atencoding a video clip/segment to a target bit rate accurately with high videoquality after compression. Among the various models used by HEVC rate controlalgorithms, the R-${\lambda}$ model performs the best in both coding efficiencyand rate control accuracy. However, compared with encoding with a fixedquantization parameter (QP), even the best rate control algorithm [1] stillunder-performs when comparing the video quality achieved at identical averagebit rates. In this paper, we propose a novel generalizedrate-distortion-${\lambda}$ (R-D-${\lambda}$) model for the relationshipbetween rate (R), distortion (D) and the Lagrangian multiplier (${\lambda}$) inrate-distortion (RD) optimized encoding. In addition to the well designedhierarchical initialization and coefficient update scheme, a new model basedrate allocation scheme composed of amortization, smooth window and consistencycontrol is proposed for a better rate allocation. Experimental resultsimplementing the proposed algorithm in the HEVC reference software HM-16.9 showthat the proposed rate control algorithm is able to achieve an average of BDBRsaving of 6.09%, 3.15% and 4.03% for random access (RA), low delay P (LDP) andlow delay B (LDB) configurations respectively as compared with theR-${\lambda}$ model based RC algorithm [1] implemented in HM. The proposedalgorithm also outperforms the state-of-the-art algorithms, while rate controlaccuracy and encoding speed are hardly impacted.

A Generalized Rate-Distortion-${\lambda}$ Model Based HEVC Rate Control Algorithm