Patent ID: 6937770

Claim:
A method of producing reduced-quality MPEG coded video from original-quality MPEG coded video, the original-quality MPEG coded video including a set of non-zero AC discrete cosine transform (DCT) coefficients for 8×8 blocks in frames of the original-quality MPEG coded video, the reduced-quality MPEG coded video also having frames of 8×8 blocks, each frame in the reduced-quality MPEG coded video having a corresponding frame in the original-quality MPEG coded video, and each 8×8 block in each frame of the reduced-quality MPEG coded video having a corresponding block in a corresponding frame in the original-quality MPEG coded video, said method comprising the steps of: selecting non-zero AC DCT coefficients from corresponding blocks in the original-quality MPEG coded video to be included in the blocks of the reduced-quality MPEG coded video so that each 8×8 block in each frame of the reduced-quality MPEG coded video has a number of bits encoding non-zero AC DCT coefficients that is generally proportional to the number of bits encoding non-zero AC DCT coefficients for the corresponding 8×8 block in the corresponding frame of original-quality MPEG coded video; which includes computing a number of bits available for encoding the non-zero AC DCT coefficients in said each of the 8×8 blocks in each frame of the reduced-quality MPEG coded video, the number of bits available for encoding being computed by scaling the number of bits encoding non-zero AC DCT coefficients in the corresponding block of the corresponding frame of the original-quality MPEG coded video by a scale factor for said each frame, the scale factor being selected to obtain a desired reduced bit rate in the MPEG coded video for said each frame; and which includes computing a moving average of frame size of the frames in the original-quality MPEG coded video, and computing the scale factor for said each frame from the moving average of frame size and a desired frame size for the reduced-quality MPEG coded video.