US Patent 7711052 Video coding

A method of encoding a video signal representing a sequence of pictures, the method comprising receiving a current picture for encoding, forming a temporal prediction of the current picture from a default reference picture for the current picture, comparing the default reference picture with at least one further reference picture, calculating a measure of the similarity between the default reference picture and each further reference picture and, if the measure of similarity meets a pre-determined criterion, outputting an indicator identifying the further reference picture.