pub fn b_inter_shape(mb_type: u32) -> (u8, u8, u8)Expand description
B mb_type 1..=21 → (partition layout, MV-prediction mode 0/1/2 for 16×16/
16×8/8×16, per-partition prediction direction) (spec Table 7-14).
Test-only view of [b_inter_layout] for the ENCODER crate: (mvmode, p0, p1)
with pred coded 1 = L0, 2 = L1, 3 = Bi — the encoder’s b_part_mb_type is the
exact inverse, so a round-trip over 4..=21 gates the two tables against drift.