JVET-K0346 CE4-related: One simplified design of advanced temporal motion vector prediction (ATMVP) [X. Xiu, Y. He, Y. Ye (InterDigital), H. Jang, J. Nam, S.-H. Kim, J. Lim (LG), H. Chen, H. Yang, J. Chen (Huawei)]
In this contribution, one simplified design of the advanced temporal motion vector prediction (ATMVP) tool in the BMS-1.0 is proposed to reduce both the average and worst-case complexity. The proposed method uses the aspects from CE4.2.6 Test 1 for collocated block derivation and CE4.2.5 Test 2 for adaptive ATMVP sub-block size. Compared to CE4.2.6 Test 1, the proposed method adds one early termination to avoid checking both prediction lists of all the spatial merge candidates. Moreover, for further complexity reduction, it is proposed to derive the collocated blocks for the ATMVP from the same constrained range as that used for the temporal motion vector prediction (TMVP) in HEVC.
The BD-rate results of the proposed ATMVP scheme using uncompressed motion field and 8x8 compressed motion field are provided. With uncompressed motion field, the proposed method reportedly achieves average luma BD-rate savings of 1.01% for RA, compared to the VTM-1.0 anchor. The average encoding and decoding time are 102% and 105% for RA. With compressed motion field, the corresponding BD-rate savings are 0.95% for RA with the encoding and decoding time of 102% and 105% for RA.
This contribution was initially discussed in BoG JVET-K0546 with the following recommendations:
Three modifications to BMS ATMVP were suggested,
- One fixed collocated picture is used to derive temporal motion information.
- Slice level adaptive sub-block switching, 8x8 or 4x4.
- Constrain the region from where ATMVP motion is derived to the collocated CTU plus one 4x4 block column outside the collocated CTU at the right hand side, the same region for HEVC TMVP.
Note that the first one point is the same as CE4.2.6.a, and the second point is the same as CE4.2.5.b.
It is commented that the third point could reduce the worst case memory access bandwidth.
Recommendation: Integrate the three modifications into BMS ATMVP.
It is noted that several experts support adopting the modified BMS ATMVP to VTM, some other experts request further discussion.
The BoG report was presented in Track B Sun 1230, and it was decided to adopt ATMVP to VTM, with the modifications suggested in JVET-K0346, and the version of 8x8 motion storage (which is denoted as “test 2” in section 4 of JVET-K0346v4).
Decision (VTM): Adopt ATMVP from BMS, with the modifications from JVET-K0346 as described above, and 8x8 MV storage (using always the motion information from the top left block in the 8x8 region if there are blocks smaller than 8x8).