A hybrid motion-vector coding scheme based on an estimation of the locality for motion-vector difference

The bit portion for motion-vector (MV) information becomes significant in very-low bitrate video coding as texture coding has been improved. Especially, the existing methods, such as minimum bitrate prediction (MBP)-based coding, do not work well for slow-moving video sequences, which are popular in video conferencing and videophone applications. It is because the characteristics of the video sequences are not fully exploited for the MV encoding. In this paper, we propose a new hybrid encoding scheme for MV. A new parameter called a skip rate (SR) is defined for estimating the degree of the locality for the MV difference in the proposed scheme. In addition, we suggest a joint coding with a new single codeword combined with the horizontal and vertical codewords. Either the joint coding or the MBP-based coding is determined by the SR. The simulation results show that the proposed scheme enhances the coding performance for various video sequences without additional memory.