SCTE 104/35 Codex

SCTE 104 is the link between a playout automation system and the device that injects messages into the stream. The automation system, or AS, knows the schedule and decides when a break or marker should happen; it sends a request over SCTE 104 to an Injector, which builds the actual SCTE 35 splice_info_section and injects it into the transport stream. This split matters because it keeps timing decisions with the automation system while the frame-accurate work of writing SCTE 35 stays with the Injector, and it is why most SCTE 104 message-generation requests are described in terms of the SCTE 35 output they produce. Session setup, PAMS provisioning, and Control (encryption Control Word) operations are exceptions that manage the link or configuration and produce no SCTE 35 output. In the 2004-2014 editions this overview is clause 5 rather than clause 6.