In a system for recording digital contents compressed and delivered by the
MPEG (Moving Picture Experts Group) standard, in decoding the contents,
even a DCT coefficient of the digital contents is required in a discrete
cosine transform (DCT) unit, according to the attribute information
belonging to the digital contents, of the DCT coefficients within a
block, some AC coefficients remain and the other AC coefficients are
turned to 0, and the obtained DCT coefficients are again encoded so to
create stream data for recording.