SCTE 104/35 Codex

SCTE 35 Part 2 adds an event-based layer on top of the classic message, selected when protocol_version is 1. Its clause numbers, such as the 10.3.1 event_descriptor cited here, are Part 2 numbers and can identify a different descriptor in later Part 1 documents. Its event_descriptor rides on a time_signal, optionally alongside a time_descriptor, and describes an event with a state, one of start, active, paused, resume, or fetch, and a type. The types form two hierarchies rather than one chain: a content hierarchy of network, then program, then chapter, and an advertising hierarchy of break, then opportunity, then advertisement, where advertising may sit inside or outside a program or chapter but must not overlap. Elapsed and remaining times let a receiver place itself inside an event even if it missed the start, and an extensible property list carries extra identifiers such as an adId or an eidr. For applicable linear splice events the standard sets a minimum of four seconds of advance notice (clauses 9.1 and 10.3.1), and advises aligning Part 1 and Part 2 messages across the program's splice-information PIDs, keeping each event_identifier unique across those PIDs, and holding an event's type fixed while its id is active.