A method for encoding a video sequence comprising a plurality of pictures to form encoded video data, the encoded video data comprising a picture layer and a macroblock layer, the method comprising: receiving at least one update request message from a remote video decoder, the update request message requesting an intra-coded update of video data at the picture layer; and characterised in that the method further comprises, in response to the received update request message, - measuring elapse of time from a start of transmission of the video sequence and providing an intra-coded update of video data at the picture layer if the at least one update request message is received within a predetermined period of time from the start of transmission of the video sequence and, if not, - measuring the number of update request messages received in a predetermined period of time and - providing an intra-coded update of the video data at the picture layer if more than a predetermined number of update request messages are received in the predetermined period; otherwise - providing an intra-coded update of the requested video data at the macroblock layer progressively over successive pictures of the video sequence. receiving at least one update request message from a remote video decoder, the update request message requesting an intra-coded update of video data at the picture layer; and characterised in that the method further comprises, in response to the received update request message, - measuring elapse of time from a start of transmission of the video sequence and providing an intra-coded update of video data at the picture layer if the at least one update request message is received within a predetermined period of time from the start of transmission of the video sequence and, if not, - measuring the number of update request messages received in a predetermined period of time and - providing an intra-coded update of the video data at the picture layer if more than a predetermined number of update request messages are received in the predetermined period; otherwise - providing an intra-coded update of the requested video data at the macroblock layer progressively over successive pictures of the video sequence. - measuring elapse of time from a start of transmission of the video sequence and providing an intra-coded update of video data at the picture layer if the at least one update request message is received within a predetermined period of time from the start of transmission of the video sequence and, if not, - measuring the number of update request messages received in a predetermined period of time and - providing an intra-coded update of the video data at the picture layer if more than a predetermined number of update request messages are received in the predetermined period; otherwise - providing an intra-coded update of the requested video data at the macroblock layer progressively over successive pictures of the video sequence. - providing an intra-coded update of the video data at the picture layer if more than a predetermined number of update request messages are received in the predetermined period; otherwise - providing an intra-coded update of the requested video data at the macroblock layer progressively over successive pictures of the video sequence.