Text/SW mismatch in affine fallback mode trigger (8.5.5.9)

[fbossen]

The following conditions are used to determine that the fallback mode is not triggered:
– If inter_pred_idc[ xCb ][ yCb ] is equal to PRED_BI and bxWX4 * bxHX4 is less than or equal to 225,
fallbackModeTriggered is set equal to 0.
– Otherwise, if both bxWXh * bxHXh is less than or equal to 165 and bxWXv * bxHXv is less than or equal to 165, fallbackModeTriggered is set equal to 0.

When inter_pred_idc[ xCb ][ yCb ] is equal to PRED_B, it is possible for the first condition to fail and the second condition to succeed. In SW, the second condition is never applied when inter_pred_idc[ xCb ][ yCb ] is equal to PRED_B.
For example if inter_pred_idc[ xCb ][ yCb ] is equal to PRED_B, dHorX=2048, dHorY=0, dVerX=0, dVerY=2048, then bxWX4 * bxHX4 is 289, bxWXh * bxHXh is 153, bxWXv * bxHXv is 153, and a mismatch occurs.

It is suggested to align the text with SW:
– If inter_pred_idc[ xCb ][ yCb ] is equal to PRED_BI and bxWX4 * bxHX4 is less than or equal to 225,
fallbackModeTriggered is set equal to 0.
– Otherwise, if inter_pred_idc[ xCb ][ yCb ] is not equal to PRED_BI, bxWXh * bxHXh is less than or equal to 165, and bxWXv * bxHXv is less than or equal to 165, fallbackModeTriggered is set equal to 0.

[chhuanb]

I confirmed that the spec should be fixed as suggested. The intention is to set the bounding box to bxWX4 * bxHX4 for bi-prediction, bxWXh * bxHXh and bxWXv * bxHXv for uni-prediction.

[jlchen]

Thanks for reporting the bug. This issue will be fixed in JVET-S2001-vD release.