The array mvFieldNeighbours of the class MergeCtx has overflowed.

[Haruhiko]

In the function MergeItem::importMergeInfo, the variable mergeIdx becomes larger than MRG_MAX_NUM_CANDS and overflows the array mergeCtx.mvFieldNeighbours.
This seems to occur when the function importMergeInfo is called from EncCu::addMmvdCandsToPruningList, so the value of mmvdIdx.val in the argument of mmvdMerge->importMergeInfo appears to be incorrect.

[XiangLi]

Thanks for the report. Could you provide the command line setting and encoding log of an overflow case so that we could reproduce the issue?

[fbossen]

Looks like the following shouldn't be executed when mergeItemType is equal to MergeItemType::MMVD because the value of mergeIdx is too large. Note that all these fields are set later in the function.

  if (mergeItemType != MergeItemType::GPM)
  {
    mvField[0][REF_PIC_LIST_0] = mergeCtx.mvFieldNeighbours[mergeIdx][REF_PIC_LIST_0];
    mvField[0][REF_PIC_LIST_1] = mergeCtx.mvFieldNeighbours[mergeIdx][REF_PIC_LIST_1];
    interDir = mergeCtx.interDirNeighbours[mergeIdx];
    bcwIdx = mergeCtx.bcwIdx[mergeIdx];
    useAltHpelIf = mergeCtx.useAltHpelIf[mergeIdx];
  }

[XiangLi]

Frank is right. We should not do it for MMVD. I just submitted a fix ​https://vcgit.hhi.fraunhofer.de/jvet/VVCSoftware_VTM/-/merge_requests/2626. @Haruhiko, please check whether it solves the issue. Thanks.

[Haruhiko]

The mentioned changes have resolved the overflow issue. Thank you.