Patent ID: 8804836

Claim:
A method of encoding a video stream comprising a plurality of frames, the method comprising: for each of a plurality of target image portions to be encoded in a frame, selecting a preferred one of a set of encoding modes by optimizing a function comprising an estimate of distortion for the target image portion and a measure of bit rate required to encode the target image portion, and encoding the target image portion into the encoded video stream using the selected encoding mode; transmitting the encoded video stream over a lossy channel; and maintaining an error propagation distortion map which comprises a plurality of error propagation distortion values mapping to respective frame partitions, the error propagation distortion values being based on previous encoding mode selections; wherein the estimate of distortion used to select the encoding mode for each of the target image portions is based on a corresponding portion from the error propagation distortion map; wherein said corresponding portion is constrained to being co-located with the target image portion; and wherein the method further comprises updating the error propagation distortion map after the encoding mode selection for the target image portions, and using the updated map to determine a subsequent encoding mode selection for each of the target image portions; and wherein the update of the error propagation map comprises a lower complexity calculation as a result of said constraint, relative to a case where the corresponding portion is based on a weighted sum of the error propagation distortion values from a plurality of said frame partitions.