JVET-AQ0185 AHG16: Area-ratio extension to the RDO selection count restriction [H. Bai, T. Ikai, Y. Tokumo, R. Ishimoto (Sharp)] [late]
This contribution reports on an extension to the AHG_HIC VTM based software for constraining per-CU max RDOs proposed in JVET-AP0191. In the current AHG_HIC VTM, a uniform maximum number of RDOs is applied regardless of CU size. However, it is asserted that more RDOs can be used for larger CUs in implementations. In response, the proposed extension (a.k.a. area-ratio extension) scales the per-CU max RDOs by the ratio of the CU area to an 8×8 base block, allowing larger CUs to perform a greater number of RDOs. In terms of EncT ratio vs performance balance, it is reported that the effect of this extension depends on the sequence class: For high-resolution sequences such as Class A with larger CUs, the Y BD-rate loss at the same encoding time is reduced. For sequences dominated by smaller CUs such as Class C, no improvement is observed. Based on these findings, it is recommended that the area-ratio extension be applied selectively to high-resolution content.
It was commented that also in JVET-AQ0045, the RDO budget for larger CUs is increased, but not proportional with the CU area, as in JVET-AQ0185. Even though the results of JVET-AQ0185 indicate that the impact on software runtime is not significant and even gives better results when the restriction is made less stringent, it is asserted that the motivation of the stronger restriction suggested in JVET-AQ0045 is motivated by hardware constraints.
It is also noted that the results are highly content dependent, particularly on resolution/class.
More study needed in context of AHG.