Sub-frame decoder with area dependent update rate for digital camcorder

Abstract

This invention is a method of decoding a stream of video image data transmitted as independent image frames consisting of plural marcoblocks transmitted in a nonsequential order. The method defines a sub-frame corresponding to a proper subset of the full frame. The method determines if a currently received macroblock is within the sub-frame. The method decodes the sub-frame. The sub-frame may be decoded at less than or equal to the frame rate of the video image data. A table has one entry for each macroblock that stores a transmission order within the video frame for the corresponding macroblock. The method determine if a current macroblock is within the sub-frame by reading the table. Each macroblock consists of a plurality of contiguous blocks and includes luminance data for any included blocks and chrominance data for the macroblock as a whole. The method optionally decodes the luminance data for each included block and ignores the chrominance data. The method decodes the sub-frame employing only data prior to an end of data marker or the end of a data group allocated to that block, and ignores data following an end of data marker. The method may also decode a full frame of video image data at a full frame decode rate less than the sub-frame decode rate. The method preferably employs a digital camcorder to generate the stream of video image data and a notebook computer for decoding and display.