Advanced spatial and Temporal Direct Mode for B picture coding

The direct mode in H.264/AVC can efficiently improve the coding performance of B pictures, since it exploits the spatial or temporal correlation by deriving its motion vector from previously encoded information. Therefore, it does not require any additional motion information and could save many bits. Considering the spatial and temporal correlation has not been fully exploited in the current direct mode, in this paper, we propose an advanced Spatial and Temporal Direct Mode (STDM) for B picture coding. The motion vector is selected from a set of spatial-temporal neighboring motion vectors, and the selection criterion is to minimize a spatial- temporal cost function. The framework of Decoder-side Motion Vector Derivation (DMVD) is utilized, where encoder and decoder use the same derivation process to obtain motion vectors, thus no index for the chosen motion vectors need to be coded and transmitted. Simulation results show that the proposed method significantly outperforms the current SDM and TDM in H.264/AVC.