Accessibility descriptor

The Accessibility descriptor indicates the presence of accessibility features such as AD, visual description service, or dialogue enhancement.

If the AdaptationSet includes an Accessibility descriptor that describes the type of accessible audio service being provided, the AdaptationSet provides for enhanced accessibility. The required attribute schemeIdUri is set to urn:tva:metadata:cs:AudioPurposeCS:2007, as defined in section B.1 of ETSI TS 102 822-3-1, signaling the namespace for the Accessibility descriptor.

The audio purpose classification scheme (AudioPurposeCS), which is used to describe the type of accessible audio service that is being delivered, is defined in section A.15 of ETSI TS 102 822-3-1. The value of the termID attribute shows the type of accessible audio service carried in the Dolby AC-4 bitstream, which is indicated by the value of the content_classifier parameter in the default presentation of the Dolby AC-4 bitstream, or in the AC4SpecificBox of the Dolby AC-4 audio track. The corresponding values of the termID attribute and content_classifier parameter are listed in the table.

Table 1. Corresponding termID attribute and content_classifier parameter values
termID attribute value AudioPurposeCS name content_classifier parameter value
1 Audio description for the visually impaired 010
2 Audio description for the hearing impaired 011
3 Supplemental commentary 101
4 Director's commentary 101
5 Educational notes 101
6 Main program audio 000
7 Clean feed (no effects mix) 100