Abstract
Versatile Video Coding (VVC) is the latest video coding standard jointly developed by ITU-T VCEG and ISO/IEC MPEG. In this paper, technical details and experimental results for the VVC block partitioning structure are provided. Among all the new technical aspects of VVC, the block partitioning structure is identified as one of the most substantial changes relative to the previous video coding standards and provides the most significant coding gains. The new partitioning structure is designed using a more flexible scheme. Each coding tree unit (CTU) is either treated as one coding unit or split into multiple coding units by one or more recursive quaternary tree partitions followed by one or more recursive multi-type tree splits. The latter can be horizontal binary tree split, vertical binary tree split, horizontal ternary tree split, or vertical ternary tree split. A CTU dual tree for intra-coded slices is described on top of the new block partitioning structure, allowing separate coding trees for luma and chroma. Also, a new way of handling picture boundaries is presented. Additionally, to reduce hardware decoder complexity, virtual pipeline data unit constraints are introduced, which forbid certain multi-type tree splits. Finally, a local dual tree is described, which reduces the number of small chroma intra blocks.
Highlights
T ECHNOLOGY advances of video coding become more critical as video data occupy higher traffic on the Internet and video applications demand increasing spatial and temporal resolutions
More significant losses are observed for sequences in Classes A1 and A2. These results experimentally demonstrate that increasing the maximum coding tree unit (CTU) size from 64 × 64 to 128 × 128 allows for achieving better performance for larger sequences
In [18], it is reported that compared to the HEVC reference software HM13.0 default setting, the preliminary development of the new block partitioning structure built on top of HM13.0 with quaternary tree (QT) split on, binary tree (BT) split on, ternary tree (TT) split off (TT was not proposed at that time), and CTU dual tree on, results in BD-rate reductions of 5.97% (Y), 13.89% (Cb), and 15.29% (Cr), with 158% encoding and 106% decoding runtimes under the RA condition
Summary
T ECHNOLOGY advances of video coding become more critical as video data occupy higher traffic on the Internet and video applications demand increasing spatial and temporal resolutions. Every CTU is either treated as one coding unit (CU) or split into multiple CUs. An encoder generally signals a CU split indication flag at each QT node to specify whether the current QT node is partitioned or not. For CUs of skip mode inter prediction, the PU size is fixed as 2N × 2N, and the merge scheme is applied at the PU level In this case, a merge index is conditionally signaled. In the case of intra prediction, there are two possible PU split modes for CUs: one CU can contain either one 2N × 2N PU or four N × N PUs. to avoid redundancy, the N × N PU mode is only permitted when the CU size equals the allowed minimum CU size. Only one luma intra mode is signaled for this 8 × 8 CU, while corresponding luma 4 × 4 TBs are intra predicted and transformed sequentially, using the same luma intra mode
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