This paper presents a motion-based depth estimation algorithm for automatic 2D-to-3D video conversion algorithm by employing the co-occurrence matrix of motion vectors (MVCM). Video scenes possess distinct signatures of MVCM, which enables exploiting the corresponding motion-depth relation for depth generation. The subsequent motion-compensated depth updating scheme provides stable and comfort 3D visual quality as synthesized by depth-image-based rendering. The simulation results of several high-definition image sequences indicate that the proposed algorithm produces better and more reasonable depth than two motion-based depth estimation algorithms. With the adaptive depth estimation scheme using MVCM, the proposed 2D-to-3D video conversion algorithm can accommodate a great variety of visual contents. It thus provides an efficient and reliable solution towards the problem of automatic 3D video content creation.