Temporally Dependent Rate-Distortion Optimization for AV1 Encoder

In current video coding schemes, although coding units are highly temporally exploited in the coding process, rate-distortion optimization (RDO) is performed independently with-out considering the dependency across coding blocks. This paper firstly investigates temporal multi-layer coding structure of AV1, and accordingly develops a long-term RDO model that takes into account the temporal dependencies across frames. Specifically, an impact factor of I-frame in terms of distortion propagation is first obtained, followed by the estimation of the impact factor of each frame in the multi-layer coding structure in descending order of importance. Consequently, an adaptive Lagrange multiplier determination method together with a temporally dependent RDO (TD-RDO) scheme is developed. We exemplify our method on state-of-the-art AV1 codec for testing. Experimental results show that in Random Access (RA) configuration, our proposed scheme can achieve an average of 2.07% BD-rate saving over the anchor AV1 encoder.