Video network

A packet-based video network (fig 1) comprising two or more video data sources (S1-10, fig 1), each configured to launch video data packets (figure 3A) onto the network as multicast data packets each associated with a multicast group identifier corresponding to that video data source; and a video data destination (D1-D9, fig 1) configured to receive and process video data from a video data source by joining a multicast group corresponding to that video data source, and to execute a switching operation to switch from receiving video data from a first video data source to receiving video data from a second video data source by leaving a multicast group corresponding to the first video data source and joining a multicast group corresponding to the second video data source; in which: in respect of a frame period (fig 12) during which the video data destination joins a multicast group S2 corresponding to the second video data source S2 and so receives data representing a partial or incomplete video frame B2 from the second video data source S2 , the video data destination is configured to process video data corresponding to a video frame which, at the end of that frame period, represents the most recently received video frame from the first video data source and which may be at the end of that particular frame period. The video destination circuitry may be configured not to leave the multicast group until it has received at least one whole frame of video data from the second source. The video destination circuitry may also reuse the most recent first video data source. The video data destination circuitry may comprise a first and second data buffer (figure 9) and a buffer controller.