JVET-M0002 JVET AHG report: Draft text and test model algorithm description editing (AHG2) [B. Bross, J. Chen, J. Boyce, S. Kim, S. Liu, Y. Ye]
This document reported the work of the JVET ad hoc group on draft text and test model algorithm description editing (AHG2) between the 12th meeting in Macao, CN (3–12 October 2018) and the 13th meeting in Marrakech, MA (9–18 January 2019).
At the 12th JVET meeting, it was decided to include more coding features for intra picture-prediction, inter-picture prediction, transform coefficient coding, transform, adaptive loop filtering and a tile group based high-level syntax in the third draft of Versatile Video Coding (VVC D3) and the VVC Test Model 3 (VTM3) encoding. Draft reference software to implement the VVC decoding process and VTM3 encoding method had also been developed.
The normative decoding process for Versatile Video Coding is specified in the VVC draft 3 text specification document. The VVC Test Model 3 (VTM 3) Algorithm and Encoder Description document provides an algorithm description as well as an encoder-side description of the VVC Test Model 3, which serves as a tutorial for the algorithm and encoding model implemented in the VTM3.0 software.
An issue tracker (https://jvet.hhi.fraunhofer.de/trac/vvc) was used to facilitate the reporting of errata with the VVC documents.
Nine versions of the JVET-L1001 VVC draft 3 specification text were published by the editing AHG between the 12th meeting in Macao, CN (3–12 October 2018) and the 13th meeting in Marrakech, MA (9–18 January 2019).
The specific items integrated into the text were listed in the AHG report.
The following items had been discussed within the AHG:
- Deblocking over SubCUs: There had been two different understandings of the decision from the last meeting how deblocking over SubPU boundaries is performed – recorded as "Recommendation: Apply the same logic to VVC (both ATMVP and affine) sub-blocks (on 8x8 grid) as to PU in HEVC deblocking. This means check the deblocking motion conditions for ATMVP and affine motion sub-block boundaries as if they were PUs in HEVC". The two interpretations were:
- All edges on a 8x8 sample grid can be deblocked, irrespective of the type of the edge (i.e. CU, SubCU, TU edge).
- Only Sub-CU and TU edges of a CU that is aligned on the 8x8 grid in one direction can be deblocked in the respective direction.
The current draft and the VTM-3.0 macro L0074_SUBBLOCK_DEBLOCKING followed the second understanding. However, the AHG requested JVET to discuss which solution is preferred. The following document was identified to be related:
- JVET-M0339 CE11-related: subblock boundary filter at 8x8 Grid [H. Jang, J. Nam, S. Kim, J. Lim (LGE)]
- Interaction of CPR with other newly adopted inter tools: There had been six items discussed which were related to CPR interaction with newly adopted inter tools. They were summarized as follows.
- In the current draft spec, when the first merge candidate of the current CU is coded in CPR mode, (0, 0) motion vector is used for the derivation of the collocated block, while in VTM-3.0, the next merge candidate will be examined. It was recommended to change the software to match the spec. A related contribution JVET-M0409 was noted.
- For CPR to work with the newly adopted pairwise average merging candidates, two options were discussed:
- Option 1. Disallow any combination involves CPR
- Option 2. Integrate CPR-CPR combination in draft text.
The draft spec and VTM-3.0 had implemented Option 2.
- For CPR interaction with Affine motion, neither current draft spec nor VTM-3.0 allows the combination of both being enabled at the same time. Bitstream conformance check is used in both VTM-3.0 and the current draft spec. The generation of merge candidate excludes CPR neighbours, while the generation of motion vector predictor (AMVP mode) includes CPR neighbours.
- For CPR interaction with MMVD partition, neither current draft spec nor VTM-3.0 allows the combination of both being enabled at the same time. Bitstream conformance check is used in both VTM-3.0 and the current draft spec. The generation of MMVD base motion vector excludes CPR neighbours.
- For CPR interaction with triangular partition, neither current draft spec nor VTM-3.0 allows the combination of both being enabled at the same time. Bitstream conformance check is used in both VTM-3.0 and the current draft spec. The generation of partition motion vector excludes CPR neighbours.
- For CPR interaction with CIIP, neither current draft spec nor VTM-3.0 allows the combination of both being enabled at the same time. Bitstream conformance check is used in both VTM-3.0 and the current draft spec. The generation of inter-merge motion vector includes CPR neighbours.
- The maximum number of HMVP candidates is 6, but six cases were never actually used and thus can be reduced to 5. The following document was identified to be related:
- JVET-M0436 AHG2: Regarding HMVP Table Size [J. Zhao, S. Kim (LGE)]
- Open bug tracker issues (tickets): The following tickets were suggested to need discussion:
In the JVET discussion of these items, the following outcomes were agreed:
- No action was needed on ticket #128.
- Decision (SW): A software fix was needed for #132.
- Decision (BF editorial): The downsampling of the DCT2 transform matrix should be separate horizontally and vertically (not assumed square) for #135.
Two versions of the JVET-L1002 VVC Test Model 3 (VTM 3) document were published by the Editing AHG between the 12th meeting in Macao, CN (3–12 October 2018) and the 13th meeting in Marrakech, MA (9–18 January 2019). The items added to VTM 3 were listed in the AHG report.
A general encoder description and some other features such as high-level syntax, the tiling mechanism and miscellaneous small coding features (such PCM mode and Delta QP signalling) had yet to be added to the document.
The AHG recommended to:
- Approve the edited JVET-L1001 and JVET-L1002 documents as JVET outputs,
- Continue to edit the VVC draft and Test Model documents to ensure that all agreed elements of VVC are fully described,
- Compare the VVC documents with the VVC software and resolve any discrepancies that may exist, in collaboration with the software AHG,
- Encourage the use of the issue tracker to report issues with the text of both the VVC specification draft and the algorithm and encoder description,
- Continue to improve the editorial consistency of VVC WD and Test Model documents,
- Ensure that, when considering the addition of new feature to VVC, properly drafted text for addition to the VVC Test Model and/or the VVC Working Draft are made available in a timely manner.