I. Introduction
After decades of development, video coding and compression technologies have achieved a tremendous progress. However, the extremely massive bandwidth and storage required by video contents are still a substantial challenge, especially when we come into the mobile Internet era with a rapid growing demand for high quality video programs. After standardizing H.264/AVC [1] successfully in 2003, experts in the ITU-T Video Coding Experts Group (VCEG) and ISO/IEC Moving Picture Experts Group (MPEG) then collaborated to finalize a new generation video coding standard, named High Efficiency Video Coding (HEVC) [2] in 2013. It is demonstrated that HEVC can achieve approximately the same subjective quality with 50% less bit-rate than H.264/AVC [3]. HEVC is a milestone in the development of video coding and compression technologies. However, a more efficient video compression scheme outperforming HEVC is eagerly desired with the explosive growth of video-oriented applications, especially when the ultra-high definition (UHD) display has become popular, even on tablets and cell-phones. To explore the future video coding technologies beyond HEVC, the Joint Video Exploration Team (JVET) was founded by VCEG and MPEG jointly in 2015. Since then, many new methods have been adopted by JVET and put into the reference software named Joint Exploration Model (JEM) [4]. In April 2018, JVET formally started the standardization of the next generation video coding standard named “Versatile Video Coding (VVC)” [5]. Compared with HEVC, VVC under development can achieve about 35% BD-rate saving on average with the random access configurations.