It seems VTM software does not support 422 chroma format.

Prior to JVET-O0050, any 4x4 CU was inferred to be INTRA predicted (or IBC). This prevented any 4x4 INTER prediction.

After JVET-O0050, any CU within a modeType == MODE_TYPE_INTER constrained region must be inter coded. This would include any 4x4 CUs. Meaning the previous approach for preventing 4x4 INTER does not work in this case.

There do not appear to be any new checks in Section 6.4.1 through 6.4.3 to prevent 4x4 CUs in MODE_TYPE_INTER regions. So, it would appear that 4x4 INTER prediction has been accidentially reintroduced.

Assuming it was not intentional for JVET-O0050 to reintroduce 4x4 INTER prediction, additional checks should be added to the "Allowed Split Processes" in Section 6.4 to prevent this.

The following issues related to the neighboring availability process in 6.4.4 need to be fixed / clarified:

Availability of neighboring blocks (below-left, top-left, right, top-right) is intended to be controlled by the array IsAvailable[ cIdx ][ x ][ y ]. This array is initialized to FALSE at the beginning of each CTU and set to TRUE for each CU after being decoded. However, this would leave the CTUs to the right and (when processed sequentially in raster scan) the CTU to the bottom-left uninitialized. In order to make sure these two CTUs are always marked as unavailable the following conditions need to be added in 6.4.4:

If one or more of the following conditions are true, availableN is set equal to FALSE: – xNbY is less than 0. – yNbY is less than 0. – xNbY is greater than or equal to pps_pic_width_in_luma_samples. – yNbY is greater than or equal to pps_pic_height_in_luma_samples. – ( xNbY >> CtbLog2SizeY ) is greater than ( xCurr >> CtbLog2SizeY ) and ( yNbY >> CtbLog2SizeY ) is greater than or equal to ( yCurr >> CtbLog2SizeY ) – ( yNbY >> CtbLog2SizeY ) is greater than or equal to (yCurr >> CtbLog2SizeY ) + 1 – IsAvailable[ cIdx ][ xNbY ][ yNbY ] is equal to FALSE. – The neighbouring block is contained in a different slice than the current block. – The neighbouring block is contained in a different tile than the current block. – sps_entropy_coding_sync_enabled_flag is equal to 1 and ( xNbY >> CtbLog2SizeY ) is greater than or equal to (xCurr >> CtbLog2SizeY ) + 1.

Furthermore, in the initialization of IsAvailable at the beginning of the Coding tree unit semantics in 7.4.11.2, the locations x0, y0 needs to be replaced by the top-left luma sample location of the current CTU:

The array IsAvailable[ cIdx ][ x ][ y ] specifying whether the sample at ( x, y ) is available for use in the derivation process for neighbouring block availability as specified in clause 6.4.4 is initialized as follows for cIdx = 0..2, x = x0..x0xCtb..xCtb + CtbSizeY − 1, and y = y0..y0yCtb..yCtb + CtbSizeY − 1: