Video coding

A transmitting terminal for encoding a video stream, the transmitting terminal comprising:

• an encoder configured to:
• cluster channels from the transmitting terminal to a plurality of receiving terminals into classes, the channels in each class having similar packet loss probabilities between the transmitting terminal and the receiving terminals of the class, and each class having an associated error propagation distortion map;
• determine an estimate of error propagation distortion for each of the classes of channels, the estimate of distortion being determined from the respective error propagation distortion map associated with each of the classes;
• and
• perform a rate-distortion optimization process comprising, for each of a plurality of target image portions to be encoded in a frame of the video stream, 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 the estimates of error propagation distortion for the classes, the encoder being arranged to encode the target image portions into an encoded version of the video stream using the selected encoding modes;
• and
• a transmitter configured to transmit the same encoded version of the video stream from the transmitting terminal to each of the plurality of receiving terminals over respective channels, the encoder being configured to use the same rate-distortion optimization process in relation to each of the plurality of receiving terminals, the use of the same rate-distortion optimization process comprising making the same encoding mode selection per target image portion based on the same optimization of said function.

A computer program product for encoding a video stream, the computer program product being embodied on a computer-readable storage memory device and comprising code configured so as when executed on a transmitting terminal to perform operations of:

• clustering channels from a transmitting terminal to a plurality of receiving terminals into classes, the channels in each class having similar packet loss probabilities between the transmitting terminal and the receiving terminals of the class, and each class having an associated error propagation distortion map;
• determining an estimate of error propagation distortion for each of the classes of channels, the estimate of distortion being determined from the respective error propagation distortion map associated with each of the classes;
• performing a rate-distortion optimization process comprising, for each of a plurality of target image portions to be encoded in a frame of the video stream, 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 the estimates of error propagation distortion for the classes;
• encoding the target image portions into an encoded version of the video stream using the selected encoding modes;
• and
• transmitting the same encoded version of the video stream from the transmitting terminal to each of the plurality of receiving terminals over respective channels, using the same rate-distortion optimization process in relation to each of the plurality of receiving terminals, the use of the same rate-distortion optimization process comprising making the same encoding mode selection per target image portion based on the same optimization of said function.