Complexity Scalable HEVC-to-AV1 Transcoding Based on Coding Tree Depth Inheritance

With the advent of the recently launched AOMedia Video 1 (AV1) bitstream specification, there is currently a need for converting legacy content encoded with the state-of-the-art High Efficiency Video Coding (HEVC) standard to the new format. However, transcoding is a complex task composed of a decoding and an encoding process in sequence, which requires long processing time and high energy consumption. This paper proposes a complexity scalable HEVC-to-AV1 transcoding solution with three operation modes, which allow adjusting the tradeoff between encoding efficiency and computational cost. The solution is based on the high correlation between block size decisions in HEVC and AV1, allowing the AV1 encoder to inherit Coding Tree depth information from the HEVC bitstream to constrain the AV1 re-encoding process. Experimental results for the three operation modes show a transcoding time reduction between 35.4% and 69.5% at the cost of a compression efficiency loss that varies between 4.9% and 16.8%.