SCTE 104/35 Codex

For linear signaling, segmentation descriptors run in program mode, so program_segmentation_flag is true. Most boundary types come as start and end pairs sharing one event id: Program, Chapter, Provider Advertisement, Distributor Advertisement, Placement Opportunity, and Unscheduled Event each have a matching Start and End. A segment stays open until its explicit end arrives; if the signaled duration elapses first, treat the segment as unclosed for reporting rather than inferring an end from the duration. That does not synthesize an end message, keep the event active, or block reuse of its id once it has expired. When a duration is present (segmentation_duration_flag is true, with the duration field carried), it defines or adjusts the expected end, and a Content Identification (0x01) descriptor can extend that end but must then carry a UPID. When two events fall at the same point in separate SCTE 35 sections, deliver the end before the new start, and give overlapping segments distinct ids so each delimiter stays unambiguous.