Audio Description/Visual Description service

If the content_classifier field of one or more audio components of a Dolby AC-4 presentation indicates Associated service: visually impaired (010), an Accessibility descriptor must be included in the referencing preselection.

For compatibility, both an Accessibility descriptor of the role scheme with the value description and an Accessibility descriptor of the audio purpose scheme with the value 1 must be included. Additionally, a Role descriptor of the role scheme with the value alternate must also be included.

<Accessibility schemeIdUri="urn:mpeg:dash:role:2011" value="description" />
<Accessibility schemeIdUri="urn:tva:metadata:cs:AudioPurposeCS:2007" value="1" />
<Role schemeIdUri="urn:mpeg:dash:role:2011" value="alternate" />

In case an adaptation set references a single-presentation Dolby AC-4 stream containing broadcast-mixed Audio Description audio, the same set of descriptors included in an Audio Description preselection must also be include in the adaptation set.