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Media Presentation Description with Dolby AC-4 Use proper values in an MPD file to describe a Dolby AC-4 bitstream. Examples of MPD files for different scenarios are provided.
Accessibility descriptorThe Accessibility descriptor indicates the presence of accessibility features such as AD, visual description service, or dialogue enhancement.

Introduction to the Dolby AC-4 in MPEG-DASH for online delivery specificationThis documentation is for online delivery (over-the-top services), specifying the required data formatting and signaling between a server (sender) and clients (receivers) to enable Dolby AC-4 to be used as an audio format within the MPEG‑DASH standard in conjunction with the ISO base media file format.
Dolby AC-4 packetization into MPEG-DASH compliant ISO base media files The process of analyzing and preparing a Dolby AC-4 bitstream for storage within an MPEG-DASH compliant ISO base media file is described. AC-4 sync frames must be converted to raw AC-4 frames before packetization.
Media Presentation Description with Dolby AC-4 Use proper values in an MPD file to describe a Dolby AC-4 bitstream. Examples of MPD files for different scenarios are provided.
- Media Presentation Description An MPD can be used to describe media presentations with one or multiple Dolby AC-4 bitstreams.
- ProfilesA profile imposes a set of specific restrictions, which are typically on features of the MPD files and segment formats.
- PeriodsMedia content can be composed of a single period or multiple consecutive media content periods.
- Adaptation sets and representationsAn adaptation set typically consists of multiple representations of the same audio, video, or A/V content. Each representation is associated with a Representation element.
- AudioChannelConfiguration descriptorThe channel configuration for a Dolby AC-4 stream is specified in the AudioChannelConfiguration descriptor.
- Accessibility descriptorThe Accessibility descriptor indicates the presence of accessibility features such as AD, visual description service, or dialogue enhancement.
- MPD for immersive stereo contentTo signal immersive stereo content in the MPD file, an additional SupplementalProperty descriptor must be included.
- ATSC 3.0 specific constraints on Media Presentation Description MPD files for ATSC 3.0 services must adhere to the constraints defined in DASH-IF Interoperability for ATSC 3.0 and the Broadcast TV Profile constraints from ISO/IEC 23009-1.
- Compatibility with ATSC 3.0 and DVB-DASHTo be compatible with ATSC 3.0 and DVB-DASH, required settings must be used for the AudioChannelConfiguration descriptor and the Accessibility descriptor.
- Media Presentation Description file examplesExample MPD files for different media presentations are provided.
Demultiplexing a Dolby AC-4 bitstream from an MPEG-DASH compliant ISO base media file segmentBuffering and parameter conflicts must be considered when product designers implement an ISO base media file format file demultiplexer that supports Dolby AC-4 bitstreams.
MPEG‑DASH and Dolby AC-4 overviewIntroduction about MPEG‑DASH and Dolby AC-4.
Glossary
Notices

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 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 valid termID values for the Accessibility descriptor and the corresponding content_classifier parameter values 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`