1. A computer implemented method of determining a motion vector for encoding a block of a predicted frame with respect to a reference frame, the method executed by a computer processor and comprising: generating a phase correlation surface between a phase correlation block of the predicted frame and a corresponding phase correlation block of the reference frame, the phase correlation block of the predicted frame including the block; selecting a variable number of phase correlation peaks on the phase correlation surface, the selected number being a function of a height of a highest phase correlation peak, each phase correlation peak associated with a motion vector, wherein the variable number of phase correlation peaks is set with respect to a fixed lower bound and a variable upper bound that is a function of an encoder quantization step size; and selecting from the motion vectors associated with the selected phase correlation peaks, a motion vector that minimizes a distortion measure between the block and a reference block offset from the block by the motion vector.