An MCMC based Efficient Parameter Selection Model for x265 Encoder

As an open-source and computationally efficient High Efficiency Video Coding (HEVC) encoder, x265 has been gaining increasing popularity in video applications. x265 provides numerous encoding parameters in view of flexibility. However, proper and efficient setting of parameters often becomes a great challenge in practice. In this paper, we deeply investigate the influence of x265 parameters based on the Slow preset and pick out important parameters in terms of efficiency and complexity. Then a Markov Chain Monte Carlo (MCMC) based algorithm is proposed for efficient parameter adaptation at the target encoding time. This paper shows that carefully selected low-complexity encoding configurations can achieve the coding efficiency comparable to that of high-complexity ones. Specifically, average 26.72% encoding time reduction can be achieved while maintaining similar Rate Distortion (RD) performance to x265 presets using the proposed algorithm.

I. Introduction

To improve compression performance relative to existing standards, new generation of video coding standards, including High Efficiency Video Coding (HEVC) [1] and Audio Video Coding Standard 2 (AVS2) [2], have been developed. HEVC has achieved about 40% bitrate reduction than its predecessor H.264/AVC at the same quality. New technologies, such as coding tree block structure and advanced motion vector prediction, have brought about great improvement on compression ratio, but they also lead to significant complexity increasement. Hence, although as the officially provided reference software of HEVC standard, HM [3] can be hardly applied to practical work directly due to its excessive high complexity.