VIDEO ENCODER HAVING REDUCED MEMORY BANDWIDTH REQUIREMENTS

A video encoder typically includes a preprocessor, a frame store, a motion compensator, and a compression module. The preprocessor converts an incoming digital video signal to image macroblocks. The frame store stores the macroblocks from anchor frames, and the motion compensator searches neighborhoods in anchor frames for best matches to macroblocks from a current frame. The compression module receives a vector from the motion compensator indicative of the best match and uses it to compress the macroblocks from the current frame. The compressed macroblocks are provided as components of a compressed video output bitstream. To perform the neighborhood search, the motion compensator accesses many neighborhood macroblocks from the anchor frame for each macroblock from the current frame. To reduce the number of memory accesses, the motion compensator caches the neighborhood macroblocks. Since the search neighborhoods for adjacent macroblocks overlap, caching is effective. The effectiveness of caching may be increased by altering the order in which macroblocks from the current anchor frame are processed. This advantageously reduces the number of neighbourhood macroblocks from the anchor frame added to the cache for each neighborhood search, thereby providing for reduced requirement for memory bandwidth of the frame store.