Prioritized reference decision for efficient motion vector coding

In the latest video coding frameworks, efficiency of motion vector (MV) coding is becoming increasingly important because of the growing bit rate portion of motion information. In this paper, we present a prioritized reference decision scheme for MV coding based on the H.264/AVC framework. This scheme makes use of a boolean indicator coded into the modified code words of mb_type and sub_mb_type, so as to designate whether the conventional median prediction or an alternative reference decision method is to be used. If the latter is indicated, a validation function is applied to a prioritized list of neighboring MVs, so that the minimum-cost MV difference (MVD) is likely to be generated using multiple reference MVs, with no extra overhead. Experimental result shows the proposed scheme achieves considerable bit rate reduction on MVDs, when compared with the conventional median prediction method. It also achieves a better and much stabler performance than the state-of-the-art MBP-based MV coding. Meanwhile, the harmful feedback issue of MBP is prevented in the proposed scheme.