JVET-P1001: Encoder / decoder deblocker mismatches for chroma QP

[bheng]

After the adoption of JVET-P1001, the chroma QP now affects the deblocking filter process. Therefore, chroma QP values must be determined, even for non-coded TUs.

However, nothing has been added in VTM software to ensure the encoder and decoder are using the same chroma QP offsets for these non-coded TUs.

Specifically, when a CU has no coded chroma residual, the encoder cannot change the chroma QP offset. In this case, the encoder must reset the chroma QP offset, in the same way the encoder currently resets the luma delta QP in corresponding situations.

For example, something equivalent to how the luma QP is reset to predicted QP when there are no residuals in xCheckDQP(). This process was not added for chroma QP when JVET-P1001 was implemented.

[bheng]

Mismatches were resolved in merge request !1229.