1. A method comprising: determining, with a video processing device, for a plurality of coded units arranged in a plurality of vectors from a portion of a video frame, a set of horizontal parameter candidates for a horizontal parameter of a global motion model for the portion of the video frame, wherein each of the horizontal parameter candidates corresponds to one of a first subset of the plurality of vectors; selecting, with the video processing device, a median value from the set of horizontal parameter candidates as the horizontal parameter of the global motion model for the portion of the video frame; determining, with the video processing device, a set of vertical parameter candidates for a vertical parameter of the global motion model for the portion of the video frame, wherein each of the vertical parameter candidates corresponds to a second subset of the plurality of vectors; selecting, with the video processing device, a median value from the set of vertical parameter candidates as the vertical parameter of the global motion model for the portion of the video frame; and processing, with the video processing device, at least one of the plurality of coded units according to the horizontal motion parameter and the vertical motion parameter.