1. A method of optimising Rate Distortion Optimisation candidate assessment in hardware apparatus, comprising: determining which Rate Distortion Optimisation candidates out of a plurality of candidates are separately processable, wherein the candidates are partitions of a picture; determining a processing delay of critical portions of candidate assessment hardware, wherein the critical portions of candidate processing hardware include a Rate Distortion Optimization Best Candidate Decision Block; a Motion Vector Predictor Calculation Block; and a Sum and Langrangian Multiplication Block; determining a rule set governing how the separately processable candidates may be ordered for processing, wherein the rule set for ordering the separately processable candidates depends on the input video resolution; determining an optimised processing order for processing the separately processable candidate assessments, dependent on the processing delay of critical portions of the candidate assessment hardware and the determined rule set; spending enough clock cycles processing other candidates in between partitions of the same size, such that the best candidate for a given partition can be set in time to calculate a motion vector difference (MVD) bit cost (RMV) for the next partition; and processing the candidates according to the determined processing order.