Motion estimation in low-delay hierarchical p-frame coding using motion vector composition

• Hierarchical P (HP) coding suffers from heavy computations in low temporal layers.
• The proposed motion vector composition strategy reduces computational complexity.
• The vector selection algorithm designed for HP coding improves RD performance.
• The algorithm merges dominant area and generates multiple composed candidates.
• More accurate composed motion vectors are obtained for HP coding.

Low-delay hierarchical prediction structure is currently adopted in various new video coding standards. The only hurdle of this structure is the need of motion estimation in distant reference frames. To maintain high coding efficiency, a large search range for motion estimation can improve the coding efficiency in distant reference pictures. Computational complexity will thus be increased dramatically. In this paper, a fast motion estimation scheme for a low-delay hierarchical P-frame structure is proposed. The proposed scheme adopts a motion vector composition strategy to expedite the motion estimation process for distant reference frames in the hierarchical P structure. In addition, a motion vector composition algorithm is tailor-made with the proposed hierarchical P coding scheme to further improve the coding efficiency. Simulation results show that the proposed scheme can deliver a remarkable complexity savings and coding efficiency improvement on coding a frame in low temporal layers of the hierarchical P structure.