US Patent 7975060 Adaptive video delivery

A video server for transmitting video across a network to a plurality of users includes a coder (112) which operates in response to call requests or instructions received across the network (102) from individual clients (104, 106). The server maintains in memory a series of user status records (116), one for each of the users. Each record includes, or refers to, a copy of a previous frame sent to the respective user. When the coder (112) receives a call request, it uses the previously-sent frame for that user to optimise coding the current frame that is to be sent, received from a frame grabber (110). The invention avoids the difficulties of video broadcasting while still requiring only a single instance of a video coder.