Down converting MPEG encoded high definition sequences to lower resolution with reduced memory in decoder loop

摘要

An MPEG encoded interlaced high definition video stream is decoded and down converted to lower resolution by an MPEG decoder with a reduced amount of reference picture memory. Received frame and field DCT coded blocks are down converted to reconstructed pixel field blocks by first converting the received frame DCT coded blocks to converted field DCT coded blocks. A vertical IDCT and a horizontal IDCT are then performed on the received field DCT coded blocks and on the converted field DCT coded blocks in order to produce residual and pixel field blocks as appropriate. The vertical IDCT is an N point vertical IDCT, and the horizontal IDCT is an M point horizontal IDCT, where N corresponds to the original block size, and where N>M. The residual and pixel field blocks are spatially filtered and down sampled vertically. IDCT, filtering, and down sampling operations are efficiently combined into single linear operators. Different horizontal and vertical minimum drift prediction filters are used to form field predictions to be added to the down sampled field residual blocks.