Abstract
This paper overviews the motion vector coding and block merging techniques in the Versatile Video Coding (VVC) standard developed by the Joint Video Experts Team (JVET). In general, inter-prediction techniques in VVC can be classified into two major groups: “whole block-based inter prediction” and “subblock-based inter prediction”. In this paper, we focus on techniques for whole block-based inter prediction. As in its predecessor, High Efficiency Video Coding (HEVC), whole block-based inter prediction in VVC is represented by adaptive motion vector prediction (AMVP) mode or merge mode. Newly introduced features purely for AMVP mode include symmetric motion vector difference and adaptive motion vector resolution. The features purely for merge mode include pairwise average merge, merge with motion vector difference, combined inter-intra prediction and geometric partitioning mode. Coding tools such as history-based motion vector prediction and bidirectional prediction with coding unit weights can be applied on both AMVP mode and merge mode. This paper discusses the design principles and the implementation of the new inter-prediction methods. Using objective metrics, simulation results show that the methods overviewed in the paper can jointly achieve 6.2% and 4.7% BD-rate savings on average with the random access and low-delay configurations, respectively. Significant subjective picture quality improvements of some tools are also reported when comparing the resulting pictures at same bitrates.
Highlights
MOTION DATA CODING IN High Efficiency Video Coding (HEVC) In HEVC, inter prediction is represented by two modes: the adaptive motion vector prediction (AMVP) mode and merge mode, wherein reference picture indices and MVDs are signaled in the former mode but not signaled in the latter one
When the current picture is with shorter absolute picture order count (POC) distance to the reference picture in list 1 than to the reference picture in list 0, the signaled MVD is directly used for list 1, otherwise, it is directly used for list 0
Encoder-only binary tree (BT) and ternary tree (TT) split constraints are needed where the general rule for merge estimation region (MER) is that any coding units (CUs) not smaller than MER size should contain one or multiple complete MERs and any CU smaller than MER size should locate within one MER entirely
Summary
In VVC, a lot of novel coding tools are developed to further improve inter prediction Those tools can be classified into two major groups, depending on whether the whole block share the same set of motion information, i.e., “whole block-based inter prediction” wherein only one set of motion information is utilized and “subblock-based inter prediction” wherein each sub-block could have its own set of motion information. Others: bidirectional prediction with coding unit weights (BCW) to introduce non-equal weights at CU level for bi-prediction [28]–[30]; motion vector compression and range to encode motion fields on reference pictures by using a 10-bit mantissa-exponent representation at every 8 × 8 grid [31] These coding tools introduced to inter prediction offer more encoding options for VVC to efficiently represent the motion fields of coded blocks with complex object motion. Toolby-tool testing results are given in Section VII to explore the coding performance and analyze the implementation complexity, and Section VIII concludes this paper
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