The notification of upcoming occurrences of events pertaining to service interactivity, in the context of a DASH streaming service, and regardless of whether that service is delivered via unicast or broadcast, is provided by the signalling of interactivity-specific event information. Such interactivity event signalling may be instantiated as a DASH Event Stream, in the form of MPD Events or in-band event messages (i.e., "emsg") as defined in ISO/IEC 23009-1 [43], or as samples in an ISOBMFF timed metadata track as defined in ISO/IEC 14496-12 [11]. As described in clause 8.8, interactivity-related events are identified by the appropriate scheme identifier such that the DASH client can forward the event metadata to the subscribing interactivity application. The 3GP-DASH client should support the event and timed metadata processing model and the WebIDL API as specified in [62]. If supported, then:

1. The processing of interactivity event signalling, and subsequent delivery of event metadata to the interactivity application shall comply with the DASH-IF's "DASH Player's Application Events and Timed Metadata Processing Model and APIs" specification [62].
2. The API between the 3GP-DASH client and consuming interactivity application, pertaining to the subscription and notification delivery of such interactivity event signalling information, shall comply with the WebIDL API as specified in [62].

The service interactivity application could be implemented as either a native application or a Web application.