JVET-C0047 Generalized bi-prediction for inter coding [C.-C. Chen, X. Xiu, Y. He, Y. Ye (InterDigital)]

This proposal presents a generalized bi-prediction (GBi) mode that allows bi-prediction weights to be signalled at the CU level and used for the bi-predicted PUs in that CU. The candidate set of weights in the GBi mode includes a total of 7 weights, including the value 0.5 which corresponds to the conventional bi-prediction mode. An index pointing to the entry position of a weight value in the candidate weight set is proposed to be signalled. At most one index per CU is signalled, and the corresponding weight values are shared across all the PUs and all colour components in that CU. When compared with the JEM-2.0 anchor, GBi reportedly performs consistently better in all test cases, with average Y BD-rate reduction of 1.0% for Random Access cases and 1.0% for Low Delay B cases.

The Powerpoint deck used when presenting the proposal had some additional slides compared to the uploaded word file version.

There were significant increase in encoding time (>300%)

One configuration uses a negative weight. Further study of the impact of different weights would be interesting.

It is commented that the gain is practically equal when using the tool with the HM or JEM, which indicates that there is no conflict with other coding tools.

Further study in an EE was planned. Reduction of encoder complexity and alignment with QTBT need to be investigated.