Caption service descriptor [ATSC Semantics]

The caption service descriptor provides closed captioning information, such as closed captioning type and language code for events with closed captioning service.

If there is a captioning service during some portion of an event, the caption_service_descriptor must appear in the descriptor field for the Event Information table (EIT) event. If there is no captioning service during an EIT event, no caption_service_descriptor shall be present for that event.

The caption_service_descriptor may optionally also be present in the Program Map Table for the MPEG-2 program service that corresponds to the Event Information Table. If present in the Program Map Table, the caption_service_descriptor should be located in the ES_info field for the video elementary stream and should match the values in the currently applicable event listed in the Event Information Table (EIT).

For analog captions, (digital_cc = 0), the three bytes of the language field, and the easy_reader and wide_aspect_ratio fields have no meaning. In addition, the line21_field has been deprecated in the most recent versions of the ATSC A/65 [PSIP] standard and may be set or clear. Previously, this field indicated whether the analog captions were to be found on the 'even' or 'odd' video field.

NOTE: This page was modified on July 2, 2009, to correct the previous positioning of the easy_reader and two following fields, to clearly identify the inner loop, and to add explanatory language.

See: Descriptors Generally