1. A method of encoding a downsampled video, wherein the downsampled video is a spatially downsampled version of a full-resolution video, the downsampled video including a frame having a macroblock partitioned into at least one partition, one partition of the at least one partition corresponding to at least two full-resolution partitions in a corresponding frame of the full-resolution video, each of the at least two full-resolution partitions having an associated full-resolution motion vector relative to a reference frame, the method comprising: downscaling the associated full-resolution motion vectors; calculating a weighting factor for each of the downscaled full-resolution motion vectors, wherein each weighting factor is based upon transform domain residual coefficients associated with that full-resolution motion vector; determining a motion vector prediction as the average of the product of each of the downscaled full-resolution motion vectors with its respective weighting factor; selecting a desired motion vector for said one partition from a search area within the reference frame, the search area being centered at a point indicated by the motion vector prediction; and encoding the downsampled video to generate an encoded downsampled video, including the desired motion vector for said one partition, wherein there are k full-resolution partitions, and for each i th downscaled full-resolution motion vector said calculating comprises calculating the corresponding weighting factor w i in accordance with the expression: w i =  D ⁢ ⁢ C i  + ∑ ∀ j ∈ TCOEF ⁢ ⁢ s ⁢ ⁢ _ ⁢ ⁢ A ⁢ ⁢ C ⁢  A ⁢ ⁢ C i , j  ∑ ∀ m ∈ k ⁢ (  D ⁢ ⁢ C m  + ∑ ∀ j ∈ TCOEF ⁢ ⁢ s ⁢ ⁢ _ ⁢ ⁢ A ⁢ ⁢ C ⁢  A ⁢ ⁢ C m , j  ) wherein DC i is the DC transform domain residual coefficient of the i th full-resolution partition, and AC i,j is the j th AC transform domain residual coefficient of the i th full-resolution partition, j being an index from 1 to the number of transform domain residual AC coefficients associated with the i th full-resolution partition, and m being an index from 1 to k.