The Joint Collaborative Team on Video Coding (jct-vc) of itu-t wp3/16 and iso/iec jtc 1/ sc 29/ wg 11 held its tenth meeting during 11-20 July 2012 at the City Conference Centre (ccc), a k. a

5.18Memory bandwidth reduction (4 – done - Revisit)

Summary of action taken: disable bipred syntax for 8x4/4x8

JCTVC-J0086 AHG7: Disallow bi-predictive mode for 8x4 and 4x8 inter PUs [M. Zhou (TI)]

In the current HM7.0 design an encoder is allowed to send bi-predictive motion vectors for inter PUs of 8x4 and 4x8 and a decoder discards list 1 motion vectors for those PUs in order to reduce the worst case memory bandwidth requirements of motion compensation. Such a design may cause design confusion on the encoder side and unnecessarily complicate the decoder design validation. This contribution advocates to prohibit bi-predictive motion vectors for inter 8x4 and 4x8 PUs by modifying the CABAC binarization of inter_pred_idc. In the proposed algorithm, the CABAC binarization of inter_pred_idc for inter 8x4 and 4x8 PUs is modified to (FL, cMax = 1), i.e. “1” for Pred_L1 and “0” for Pred_L0, and for inter PUs of size 8x8 and above the same CABAC binarization process defined in HM7.0 is used, i.e. “1” for Pred_BI, “01” for Pred_L1 and “00” for Pred_L0. Compared to HM7.0, the proposed algorithms leads to an average gain of 0.0/0.0/0.1/0.1% (in RA-Main/RA-HE10/LB-Main/LB-HE10). Prohibiting bi-pred mode for 8x4 and 4x8 inter-PUs at syntax level is helpful for avoiding potential confusions from both encoder and decoder side.

Decision: Adopt.