Complementary Motion Vector for Motion Prediction in Video Coding with Long-Term Reference

In HEVC, there are two types of motion vector (MV) when long-term reference is enabled: short-term MV (SMV) pointing to short-term reference frame and long-term MV (LMV) pointing to long-term reference frame. And cross-class prediction between SMV and LMV is not allowed because of their low correlation. Therefore, MV predictor candidates of current block would be inadequate when neighboring MVs are in different types. This paper proposes a complementary MV to enrich MV predictor candidates for current block. There would be two types of MV for each neighboring inter block. In addition to MV used in motion compensation, a complementary MV of the other type is derived by reconstructed pixels. This paper also proposed a reliability-based MV predictor candidate list construction method to improve the prediction efficiency of complementary MVs. Experimental results show that the proposed method can achieve 1.18% coding performance improvement on average.