Complexity-scalable HEVC-to-AV1 video transcoding based on partition inheritance

After the AOMedia Video 1 (AV1) bitstream specification was launched by the Alliance for Open Media, the need for converting legacy content encoded with the state-of-the-art High Efficiency Video Coding (HEVC) standard to the new format has arisen in several scenarios. However, transcoding is a complex task composed of a decoding and an encoding process in sequence, which requires long processing times and high energy consumption. This paper presents a complexity-scalable HEVC-to-AV1 transcoding scheme, which comprises 25 configuration modes chosen based on a Pareto Optimization strategy and built upon the correlation between block size decisions in HEVC and AV1. The configurations allow the AV1 encoder to inherit partitioning information from the HEVC bitstream to constrain the AV1 reencoding process, thus speeding up the transcoding operation. Experimental results showed that the proposed transcoding complexity reduction ranges from 0.41 up to 35.06%, on average, with coding efficiency losses that vary between 0.0536 and 5.3801%.