Broadcast metadata [EtherGuide Glossary]
Probably the slimiest term in computing is metadata. Metadata is simply data that describes other data. Before your mind goes mushy from thinking too much about that absurdism, in the case of audio/video and data broadcasting, metadata is data that describes the essence -- audio, video and data streams -- that make up programs.
There is a large amount of metadata used in planning, producing and presenting television and radio programs. Cameras might record not only the date and time that a clip was filmed, but could also include all video and audio settings, the camera's location (from an internal GPS device), the direciton in which it is pointing. Production metadata could even include the labels on old-fashioned film cannisters and tape cases. Fortunately for us, virtually none of that metadata is broadcast metadata.At least none of it is broadcast metadata at this point.
To qualify as broadcast metadata, the metadata must be included in the transmitted transport stream. In the MPEG-2 world, there is mandatory and optional metadata.
Mandatory and optional broadcast metadata
If a transport stream has audio/video content, each of the "program services" must be described in an MPEG-2 Program Map table, and each of the Program Map tables must be listed in a Program Association table. So, if a transport stream is to be useful in any way, these tables are mandatory.
ATSC specifications make additional broadcast metadata mandatory for ATSC-compliant transport streams.