1. A method of encoding a video, the video including a plurality of frames including a target frame and an original reference frame, the original reference frame having been encoded and decoded to produce a reconstructed reference frame stored in a frame store, the target frame including an inter-coded partition, the method comprising: selecting a predicted motion vector for the inter-coded partition; calculating predicted residual values from the difference between the inter-coded partition and a reference block in the original reference frame, wherein the reference block is identified by the predicted motion vector; and determining an actual motion vector with reference to the reconstructed reference frame using a rate-distortion expression incorporating the predicted residual values.