SCTE 104/35 Codex

How long the segment runs, counted in ticks of the 90 kHz clock, so 90,000 ticks is one second. It is present only when the duration flag is true, and it indicates the expected end of the segment; a receiver should still wait for the explicit closing message rather than inferring the end from the duration alone, and some segment types add their own duration rules. When a duration is carried on an end message it must be zero, but an end message may also omit it entirely.