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Descriptors [MPEG Semantics]

 

Descriptors are (generally) optional, variable-length data elements that can add standards-defined or user-defined data elements to MPEG-2 private table sections.

 

The MPEG-2 specification (ISO/IEC 13818) defines many descriptors, as do various specifications published by ATSC, DVB, SCTE and ARIB. Some of these specifications mandate that a particular descriptor be found at a specific location in a specified private table. Generally, there are few restrictions on descriptors, to the extent that DVB-, ARIB- or SCTE-specified descriptors can be found in ATSC private tables, and vice-versa.

 

Every descriptor has the same format. The first byte is the descriptor tag, followed the descriptor_length with a value of zero to 255 that specifies how many bytes are in the descriptor to follow, then the descriptor's data.

 

Generally, tables that permit descriptors have two or more locations to place descriptors, which are called "descriptor loops", amounting to an "inner" and "outer" descriptor loop.

 

Note: there is no specified order in which descriptors must or should appear with a particular descriptor loop, and there is no significance to the order that descriptors appear within a particular descriptor loop.

 

MPEG transport stream descriptors
tag D/HexNamelocationsmax per loopreference
0 / 0x0Reserved
1 / 0x1Reserved
2 / 0x02video_stream_descriptor  13818-1
3 / 0x03audio_stream_descriptor  13818-1
4 / 0x04hierarchy_descriptor  13818-1
5 / 0x05registration_descriptor (ATSC=1)13818-1
6 / 0x06data_stream_alignment_descriptor  13818-1
7 / 0x07target_background_grid_descriptor  13818-1
8 / 0x08video_window_descriptor  13818-1
9 / 0x09CA_descriptor  13818-1
10 / 0x0AISO_639_language_descriptor  13818-1
11 / 0x0Bsystem_clock_descriptor  13818-1
12 / 0x0Cmultiplex_buffer_utilization_descriptor  13818-1
13 / 0x0Dcopyright_descriptor  13818-1
14 / 0x0Emaximum_bitrate_descriptor  13818-1
15 / 0x0Fprivate_data_indicator_descriptor  13818-1
16 / 0x10smoothing_buffer_descriptor  13818-1
17 / 0x11STD_descriptor  13818-1
18 / 0x12IBP_descriptor  13818-1
27 / 0x1BMPEG-4_video_descriptor  13818-1
28 / 0x1CMPEG-4_audio_descriptor  13818-1
29 / 0x1DIOD_descriptor  13818-1
30 / 0x1ESL_descriptor  14496-1
31 / 0x1FFMC_descriptor  13818-1
32 / 0x20External_ES_ID_descriptor  13818-1
33 / 0x21MuxCode_descriptor  13818-1
34 / 0x22FmxBufferSize_descriptor  14496
35 / 0x23MultiplexBuffer_descriptor  14496
36 / 0x24FlexMuxTiming_descriptor  14496
19 - 63
0x13-0x3F
Reserved
74-255
0x40-0xFF
User Private

 

See: Descriptors Generally

 

This page was last modified on October 13, 2009 to provide clarification about the order of descriptors within a loop.

 

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