4. A video memory according to claim 1, in which said at least one ancillary data word associated with each input video data block comprises an error flag indicative of a data error in said input video data block.
4. A video memory according to claim 1, in which said at least one ancillary data word associated with each input video data block comprises an error flag indicative of a data error in said input video data block. 5. A video memory according to claim 4, further comprising means for rewriting at least a part of said at least one ancillary data word in a modified form from said recirculating buffer into said video store.