Method and apparatus for decoding video data

The present invention relates to the decoding of video bit-streams, particularly although not exclusively encoded according to International Standard ISO/IEC 13818-2 (commonly referred to as MPEG-2 video). A video decoder for decoding video pictures encoded according to the MPEG-2 standard, having reduced memory requirements, including a memory for storing means for storing a plurality of anchor frames, the decoder employing such anchor frames to generate B-frames, and including block-to-raster buffer means for holding B-frame data for display, the decoder being operable in first and second modes of operation,wherein in a first mode of operation a picture is encoded as a single frame and the video decoder decodes the entire frame twice wherein in a first decoding a set of lines of a first field are provided to the buffer for display, whereas in a second decoding lines from a second field are provided to the buffer for display; andwherein in a second mode of operation in which two consecutive field pictures of a frame are decoded, a first field picture is decoded and provided to the buffer means for display, and then a second field picture is decoded and provided to the buffer means for display. In order to reduce memory requirement still further, data can be stored in the buffer in any available memory location, the addresses of the locations being held in a pointer table.