MPEG-2 Descriptors Generally
descriptors are variable-length byte arrays that extend the functionality in MPEG-2 private table sections. Some descriptors are limited in purpose and scope, and others have wide utility.
Descriptors are published by MPEG and by other bodies that are coordinated with MPEG descriptors but might interfere with one another. These "MPEG users" are ARIB, ATSC, DVB and SCTE.