Patent ID: 6438168
Filing Date: 2002-08-20
Classification: H04N

Abstract:
A method of bandwidth scaling of a compressed video stream comprising the steps of:(A) decompressing an original previously compressed video stream image having a first level of compression including a first level of quantization, said original video stream comprising a set of original motion pictures; said original video stream image comprising a set of original macro blocks; said set of original macro blocks further comprising a set of I source pictures, a set of P source pictures, and a set of B source pictures; said decompressed video stream image comprising a set of decompressed motion pictures; said decompressed video stream image comprising a set of decompressed macro blocks; said set of decompressed macro blocks further comprising a set of I decompressed pictures, a set of P decompressed pictures, and a set of B decompressed pictures; said step (A) further comprising the steps of: (A1) recovering and saving a set of original motion vectors for each said P source picture and each said B source picture; wherein each said original motion vector substantially points out to at least one macro block in said original video stream; and (A2) recovering a reconstructed original video stream; wherein said reconstructed original video stream differs from said original video stream by an amount of information lost during an original compression process of said original video stream; said reconstructed original video stream comprising a set of reconstructed original macro blocks; said set of reconstructed original macro blocks further comprising a set of I reconstructed source (RS) pictures, a set of P reconstructed source (RS) pictures, and a set of B reconstructed source (RS) pictures; and (B) re-compressing said decompressed video stream image to create a re-compressed video stream image having a second level of compression including a second level of quantization, wherein said second level of compression is higher than said first level of compression, and wherein said second level of quantization is stronger than said first level of quantization, said re-compressed video stream image comprising a set of re-compressed motion pictures; said re-compressed video stream image comprising a set of re-compressed macro blocks; said set of re-compressed macro blocks further comprising a set of I destination pictures, a set of P destination pictures, and a set of B destination pictures; said step (B) further comprising the steps of: (B1) processing said set of recovered and saved original motion vectors for each said P source picture and each said B source picture in order to create a set of usable source motion vectors for each said P destination picture and each said B destination picture; (B2) removing an interframe redundancy from each said P (RS) picture and from each said B (RS) picture by using said set of usable source motion vectors, wherein the values of a set of pixels in each said I (RS) picture is independently provided, and wherein in each said P (RS) picture, only the incremental changes in each said pixel value from a preceding I (RS) picture or a preceding P (RS) picture are coded, and wherein in each said B (RS) picture, a set of pixel values are coded with respect to both an earlier I (RS)/or P (RS) picture, and a later I (RS)/or P (RS) picture; (B3) removing intraframe redundancy by performing a 2-dimensional discrete cosine transform (DCT) on a plurality of 8Ã—8 values matrices to map the spatial luminance or chrominance values into a frequency domain; (B4) performing a quantization process having said second level of quantization of each DCT coefficients by weighting each element of each said 8Ã—8 value matrix in accordance with its chrominance or luminance type and its frequency; (B5) performing a run length coding for each said weighted element of each said 8Ã—8 valve matrix without information loss as an ordered list of a â€œDCâ€  block coefficient; and alternating pairs of a non-zero â€œACâ€  value and a length of zero elements following said non-zero â€œACâ€  value; wherein each said element of one said matrix is presented as if said matrix is read in a zigzag manner; and (B6) performing an entropy encoding scheme for each said (RS) video stream in order to further compress the representations of each said DC block coefficient and each AC value-run length pairs using variable length codes; wherein each said original de-compressed video stream is re-compressed by using said set of reusable source motion vectors; wherein said step (B1) of processing said set of recovered and saved original motion vectors for each said P source picture and each said B source picture further includes the steps of: reducing the differences of the quantization level for each pair of a P source picture/corresponding P destination picture at a first predetermined amount; reducing the differences of the quantization level for each pair of an I source picture/corresponding I destination picture at a second predetermined amount; and increasing the quantization level for each destination B picture at a third predetermined amount to compensate for the reduction in the quantization level for each pair of an I source picture/corresponding I destination picture, and for each pair of a P source picture/corresponding P destination picture in order to preserve said second compression level; wherein said reduction of the differences of the quantization level for each pair comprising an I source picture and a corresponding I destination picture by said first predetermined amount; and for each pair comprising a P source picture and a corresponding P destination picture by said second predetermined amount reduces the propagation of errors caused by re-using a plurality of motion vectors originally used for a plurality of source pictures compressed at said first quantization level for a plurality of destination pictures compressed at said second quantization level.