JVET-M0128 AHG17: On reference picture management for VVC [Y.-K. Wang, Hendry (Huawei), S. Deshpande (Sharp), M. M. Hannusela (Nokia), G. Ryu, W. Choi (Samsung), X. Wang, Y.-W. Chen (Kawi), L. Zhang (Bytedance), P. Wu, M. Li (ZTE), S.-H. Kim (LG), J. Boyce (Intel), A. M. Tourapis, D. Singer (Apple), F. Edouard, P. Andrivon (Technicolor), Y.-W. Huang, C.-W. Hsu, C.-Y. Chen, T.-D. Chuang, L. Chen (MediaTek), K. Kawamura (KDDI), Y.-C. Sun, J. Lou (Alibaba)]

After BoG discussion, this was discussed Sunday 13 January 1700 (chaired by GJS).

This contribution proposes a reference picture management approach for VVC based on direct signalling and derivation of reference picture lists 0 and 1, without use of reference picture set (RPS) as in HEVC or the sliding window plus memory management control operation (MMCO) process as in AVC.

It is asserted that the proposed approach is significantly simpler compared to the approaches in HEVC and AVC.

The proposed direct-RPL-based reference picture management approach is summarized as follows:

Two reference picture lists, list 0 and list 1, are directly signalled and derived. They are not based on RPS as in HEVC or the sliding window plus MMCO process as in AVC.

Reference picture marking is directly based on reference picture lists 0 and 1, utilizing both active and inactive entries in the reference picture lists, while only active entries may be used as reference indices in inter prediction of CTUs.

Information for derivation of the two reference picture lists is signalled by syntax elements and syntax structures in the SPS, the PPS, and the slice header. Predefined RPL structures are signalled in the SPS, for use by referencing in the slice header.

The two reference picture lists are generated for all types of slices, i.e., B, P, and I slices.

The two reference picture lists are constructed without using a reference picture list initialization process or a reference picture list modification process.

Long-term reference pictures (LTRPs) are identified by POC LSBs. When needed, additional POC LSBs are signalled for LTRPs, determined at a picture by picture basis.

In the discussion, a problem was identified with the POC MSB handling when considering random access that is not at the start of the first CVS in the “original” bitstream. Instead of signalling MSBs directly, it was suggested to use the scheme of HEVC with delta_poc_msb_present_flag[ i ] and delta_poc_msb_cycle_lt[ i ] (and remove the proposed additional MSB length syntax in the PPS).

In the discussion, it was noted that there should be a POC wrap-around prevention constraint for short-term pictures (see HEVC C.4 item 8). It was agreed that this is needed.

Decision: Adopt with modifications as described above.