Accessibility descriptor
If the adaptation set provides for enhanced accessibility, the AdaptationSet may include an accessibility descriptor
that describes the type of accessible audio service being provided. The required attribute
schemeIdUri must be set to urn:tva:metadata:cs:AudioPurposeCS:2007, as defined in
section B.1 of ETSI TS 102 822-3-1 v1.4.1, 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 v1.4.1. The value of the termID
attribute must be set to match the type of accessible audio service carried in the Dolby Digital
Plus bitstream, which is indicated by the value of the
bsmod parameter in independent substream 0 of
the Dolby Digital
Plus stream, or in the EC3SpecificBox of the Dolby Digital
Plus audio track. The corresponding values of the termID attribute and bsmod parameter are listed in the table.
| termID attribute value | AudioPurposeCS name | bsmod 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
|