Beyond regular audio and video support, TV programs typically also require support for auxiliary components such as subtitles and closed captioning, often due to regulatory requirements. DASH-IF IOP provides tools to addresses these requirements. We collect them here.
Signalling for the closed caption services is provided by including Accessibility descriptors. The Accessibility descriptor is included for the AdaptationSet and all included Representations shall provide equivalent captions. The @value attribute of each descriptor can be either list of languages or a complete map of services (or CC channels, in CEA-608 terminology).
||DASH-IF IOP v3.3||Section 18.104.22.168||Used for signaling of CEA-608 caption services. The Accessibility descriptor shall be provided with @schemeIdURI set to urn:scte:dash:cc:cea-608:2015, and an optional @value attribute to describe the captions. If the @value attribute is not present, the Representation contains a CEA-608 based closed captioning service. The options for the @value attribute is further described in the reference.|