In section 9.3.4.2.2 "Derivation process of ctxInc using left and above syntax elements", the spec says:

For the syntax elements alf_ctb_flag[ cIdx ][ ctbX ][ ctbY ], alf_ctb_cc_cb_idc[ ctbX ][ ctbY ], and alf_ctb_cc_cr_idc[ ctbX ][ ctbY ], ... cIdx equal to 1 for alf_ctb_cc_cr_idc[ ctbX ][ ctbY ] and cIdx equal to 2 for alf_ctb_cc_cr_idc[ ctbX ][ ctbY ].

...

The location ( xNbL, yNbL ) is set equal to ( x0 − 1, y0 ) and the derivation process for neighbouring block availability as specified in clause 6.4.4 is invoked with the location ( xCurr, yCurr ) set equal to ( x0, y0 ), the neighbouring location ( xNbY, yNbY ) set equal to ( xNbL, yNbL ), checkPredModeY set equal to FALSE, and cIdx as inputs, and the output is assigned to availableL.

However, in the VTM code for CABACReader.cpp:

void CABACReader::ccAlfFilterControlIdc(CodingStructure &cs, const ComponentID compID, const int curIdx,
                                        uint8_t *filterControlIdc, Position lumaPos, int filterCount)
{
  RExt__DECODER_DEBUG_BIT_STATISTICS_CREATE_SET( STATS__CABAC_BITS__CROSS_COMPONENT_ALF_BLOCK_LEVEL_IDC );

  const Position leftLumaPos  = lumaPos.offset(-(int) cs.pcv->maxCUWidth, 0);
  const Position aboveLumaPos = lumaPos.offset(0, -(int) cs.pcv->maxCUWidth);

  const uint32_t curSliceIdx = cs.slice->getIndependentSliceIdx();
  const TileIdx  curTileIdx  = cs.pps->getTileIdx(lumaPos);

  const bool leftAvail =
    cs.getCURestricted(leftLumaPos, lumaPos, curSliceIdx, curTileIdx, ChannelType::LUMA) != nullptr;
  const bool aboveAvail =
    cs.getCURestricted(aboveLumaPos, lumaPos, curSliceIdx, curTileIdx, ChannelType::LUMA) != nullptr;
  ...

the availability uses ChannelType::LUMA.

This means that the VTM code is equivalent to if the spec set cIdx equal to 0 for alf_ctb_cc_cr_idc and alf_ctb_cc_cr_idc.

I believe the availability depends on cIdx, so this is not just an implementation detail.

Caused by null SPS in coding structure when intra coding using e.g.

bin/EncoderAppStatic -c cfg/encoder_intra_vtm.cfg -c cfg/per-sequence/RaceHorsesC.cfg -f 1 -q 37 -b out.bin --DualITree=0

Crash also occurs for RGB content in non-420 and HBD CTCs. Merge request "Fix SPS crash for RGB content" submitted with proposed fix.

Similar fix applied for inter coding in "Fix crash for class F: set SPS in CodingStructure"

Some syntax elements of NNPFC are not initialised in SEI.h

If the default constructor is used to create an NNPFC SEI message in different machines, this is likely to result on non-matching bitstreams.