In this paper, we propose a new approach for estimating global motions from a coarsely sampled motion vector field. The proposed method minimizes the fitting error between the input motion vectors and the motion vectors generated from the estimated motion model using the Newton-Raphson method with outlier rejections. Applications of the proposed method in video coding include fast global motion estimation for MPEG-4 Advanced Simple Profile (ASP) coding, MPEG-2 to MPEG-4 ASP transcoding, and error concealment of motion vectors. Simulation results and analyses are provided for the proposed method and applications, which show the accuracy and robustness of the proposed algorithm.