Video coding

A method according to any preceding claim wherein the indicator is included in a picture header.

A method according to any preceding claim wherein the video signal is encoded according to the H.263 video compression standard and the indicator is included in the Supplemental Enhancement Information.

A method according to any preceding claim wherein the comparison is carried out for portions of a picture at a time.

A method of encoding a video signal representing a sequence of pictures, the method comprising receiving a current picture for encoding, forming a prediction of at least part of the current picture from a default reference picture for the current picture, comparing the part of the default reference picture or the current picture with a corresponding part of at least one further picture of the sequence to form a measure of similarity and, if the measure of similarity meets a pre-determined criterion, outputting an indicator in respect of the part of the current frame identifying the further picture of the sequence.

A method of decoding an encoded video signal representing a sequence of pictures, the encoded signal including pictures that have been encoded by forming a temporal prediction of a current picture from a default reference picture for the current picture, the method comprising receiving an encoded video signal representing a current picture and decoding at least the picture header of the current picture wherein, when the decoder is unable to decode the default reference picture of the current picture, examining an indicator identifying a further reference picture and decoding the current picture with reference to said further reference picture if such an indicator is associated with the current picture.

A video encoder comprising an input for receiving a video signal representing a sequence of pictures, an input for receiving a current picture for encoding, a predictive coder for forming a temporal prediction of the current picture from a default reference picture for the current picture, a comparator for comparing the default reference picture or the current picture with at least one further reference picture and calculating a measure of the similarity and, when the measure of similarity meets a pre-determined criterion, outputting an indicator identifying the further reference picture.

A video decoder comprising an input for receiving an encoded video signal representing a sequence of pictures, the encoded signal including pictures that have been encoded by forming a temporal prediction of a current picture from a default reference picture for the current picture, the decoder comprising an input for receiving an encoded video signal representing a current picture and a processor for decoding at least the picture header of the current picture wherein, when the decoder is unable to decode the default reference picture of the current picture, the decoder is arranged to examine an indicator identifying a further reference picture and to decode the current picture with reference to said further reference picture if such an indicator is associated with the current picture.