Patent ID: 9338473
Filing Date: 2016-05-10
CPC Classification: H04N

Claim Text:
1. A method of encoding a video stream at an encoder of a transmitting terminal for transmission over a lossy channel to a decoder at a receiving terminal, the method comprising: performing a rate-distortion optimization process comprising, for each of a plurality of target image portions to be encoded in each of a plurality of frames, 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, the estimate of distortion being based on source coding distortion and an estimate of a distortion that would be experienced due to possible loss over the channel, the rate-distortion optimization process for a current one of said frames being performed in dependence on feedback received from the receiving terminal based on an earlier one of said frames; encoding the target image portion into the encoded video stream using the selected encoding mode; transmitting the encoded video stream over the channel; running an encoder-side instance of the decoder at the encoder, and maintaining at the encoder a decoded picture buffer storing error propagation distortion maps associated for each frame that is stored in the decoded picture buffer; updating the error propagation distortion maps based on said feedback for use in each respective subsequent encoding mode selection, said updating effective to improve rate-distortion performance; the set of encoding modes including a non-acknowledged long-term reference inter prediction mode which encodes the target image portion relative to a corresponding long-term reference in an unacknowledged frame or part of a frame stored in the decoded picture buffer; and performance of the rate-distortion optimization process in dependence on said feedback comprises determining a weighted estimate of distortion due to loss in dependence on an estimated probability of loss and a time since a last acknowledged earlier frame or acknowledged part of an earlier frame.