A system comprising a video storage node, a video replay node, and a communications network means arranged to operably couple the video storage node and the video replay node; the video storage node being arranged to store video data, and to transmit stored data via the communications network means; the video replay node being arranged to receive via the communications network means video data transmitted by the video storage node, and to render an image therefrom; wherein the video storage node has transmit buffer means for temporarily retaining stored video data, and the video replay node has a receive buffer means for temporarily retaining said video data received thereby, characterized in that: the system further comprises transmission control means for detecting at the video replay node when the content value of the receive buffer means thereof matches or exceeds a predetermined upper content value and for communicating such detection via the network to the video storage node as a first detection signal; and the video storage node is operable to transmit video data to the video replay node only if the content of the transmit buffer means matches or exceeds a predetermined lower content value and the content of the receive buffer means does not exceed the predetermined upper content value, the video storage node being operable to complete transmission of video data corresponding to a whole video frame to the video replay node if transmission of such data has commenced before receipt of the first detection signal; wherein the predetermined upper content value corresponds to the content of the receive buffer means when a predetermined portion of the buffer capacity is unused and the predetermined portion is sufficient to contain an amount of content equal to twice the product of: the maximum rate of video data transmission supported by the communications network means and the duration of a whole video frame at a video renderer of the video replay node. the system further comprises transmission control means for detecting at the video replay node when the content value of the receive buffer means thereof matches or exceeds a predetermined upper content value and for communicating such detection via the network to the video storage node as a first detection signal; and the video storage node is operable to transmit video data to the video replay node only if the content of the transmit buffer means matches or exceeds a predetermined lower content value and the content of the receive buffer means does not exceed the predetermined upper content value, the video storage node being operable to complete transmission of video data corresponding to a whole video frame to the video replay node if transmission of such data has commenced before receipt of the first detection signal; wherein the predetermined upper content value corresponds to the content of the receive buffer means when a predetermined portion of the buffer capacity is unused and the predetermined portion is sufficient to contain an amount of content equal to twice the product of: the maximum rate of video data transmission supported by the communications network means and the duration of a whole video frame at a video renderer of the video replay node.