SCTE 104/35 Codex

Pre-roll is how far ahead of the actual splice a message arrives, giving the ad system time to pick and load content and fill the decoder pipeline. SCTE 67 recommends a minimum of about four seconds for linear ad insertion, with a typical range of four to eight seconds, matching the old analog cue-tone lead time. Below the minimum a splicer may miss the avail or produce artifacts. Sending the splice_insert a few times (for example at eight, six, and four seconds) adds resilience; all copies must share the splice_event_id, later copies may refine the time, and the splicer should act on the last one that still meets the pre-roll window. SCTE 67 sets no maximum pre-roll, and a lead of more than a couple of minutes behaves as an advance announcement to clients rather than an ordinary pre-roll signal. One detail is specific to SCTE 104: its pre_roll_time is a 16-bit millisecond field, so that single field tops out near 65 seconds. That is a ceiling on the field itself, not a limit on how early a break can be announced, since a workflow can arm the injector further ahead through the timestamp() deferred-timing model.