JVET-K0102 CE4-related: Interweaved Prediction for Affine Motion Compensation [K. Zhang, L. Zhang, H. Liu, Y. Wang, P. Zhao, D. Hong (Bytedance)]

With the affine motion compensation (AMC) in the benchmark set (BMS), a coding-block is divided into sub-blocks as small as 4×4, each of which is assigned with an individual motion vector derived by the affine model. In this contribution, an interweaved prediction approach is proposed for AMC. With the interweaved prediction, a coding block is divided into sub-blocks with two different dividing patterns. Then two auxiliary predictions are generated by AMC with the two dividing patterns. The final prediction is calculated as a weighted-sum of the two auxiliary predictions. The interweaved prediction is only applied on the luma-component for affine-coded blocks with uni-prediction. Simulation results reportedly show 0.29% BD-rate savings under BMS Random Access (RA) configurations.

Multi-hypothesis prediction with two hypothesis is proposed for affine MC. Sub-block motion vectors at two sets of different sampling positions are derived and two prediction hypothesis is obtained by applying MC using the two sets of motion vectors. The two predictions are then averaged to get the final prediction.

It is applied to luma component in case of uni-prediction of affine coded blocks. So the worst case of memory access bandwidth is not changed.

It is noted that weighting matrices are designed to for combining the two prediction hypothesis.

It is noted that for boundary and corner positions in the auxiliary block partitioning patent, motion compensation is performed on 2x2 and 2x4/4x2 blocks.

A BD Rate delta of −0.3% was reported for BMS tool test.

Recommendation: Further study in a CE.