Part 1 “Accuracy specification for implementation of integer-output IDCT” specifies the IDCT accuracy that is equivalent to or extends the IEEE 1180 standard. This standard referenced by quite a few image and video compression standards had been withdrawn and MPEG needed to restore the reference.
Part 2 “Fixed-point 8×8 inverse discrete cosine transform and discrete cosine transform” specifies a particular fixed-point approximation to the ideal 8×8 IDCT and DCT function, fulfilling the 8×8 IDCT conformance requirements for the MPEG-1, MPEG-2 and MPEG-4 part 2 video coding standards.
Part 3 “Auxiliary Video Data Representation” specifies how auxiliary data such as pixel-related depth or parallax values, are to be represented when encoded by MPEG video standards in the same way as ordinary picture data.
Part 4 “Video Tool Library” contains a collection of descriptions of video coding tools, called Functional Units, as referenced in MPEG-B Part 4. Again more about this later.