Master Guide Table [ATSC Syntax]

The Master Guide table lists summary information for all other PSIP and data broadcasting tables in an ATSC transport stream, with the exception of the System Time table.

The purpose of the Master Guide Table (MGT) can be stated simply: the MGT lists summary data on PSIP (or ATSC announcement, if a station is engaged in data broadcasting) table section typess in an ATSC transport stream. There is an exception: the MGT does not list the System Time table.

Many accounts state incorrectly that the Master Guide Table must be used or is used to discover the location of certain PSIP table sections in the transport stream.  Anyone who has ever written an MPEG-2 packet demultiplexer knows the falsity of this statement; it is quite easy to extract MPEG-2 Program Specific Information and PSIP table sections from a transport stream before ever encountering a Master Guide Table section in the same stream, and only a fool would wait for the occurrence of a Master Guide Table before making use of previously-discovered table sections.

That said, the Master Guide table provides the information necessary to know (see table_type_version number, below) if a particular table type has been updated, and the number_bytes field provides a double-check to establish that a receiver has processed all the table sections of a certain type that are present in the transport stream.

The MGT, per ATSC A/65, must be injected onto the transport stream at least once per any 150 ms period.  This maximum repetition cycle is the shortest for any PSIP table, and is only 'bested' by the ATSC-compliant Program Association Table (PAT) which has a maximum repetition cycle of 100 ms.

Master Guide tables may carry optonal descriptors for any table section type (see the descriptor() field just after table_type_descriptors_length) and for the Master Guide Table section itself (see the descriptor() field just after descriptors_length).  The former descriptor location has no descriptors defined for this purpose when a PSIP table is listed, but if a private section (user-defined) is listed, an MPEG-2 registration descriptor shall be present with a format_identifier that identifies the entry with the SMPTE registration authority that applies to the particular type of table.

Semantics changed via ATSC A/81, Section 9.9.4

Note: This page was changed on August 3, 2009 to add explanatory text, and to add the previously omitted descriptor field for individual table types in the Master Guide Table, and the 'reserved', descriptor_length and descriptor field just before the CRC-32 field.