SCTE 104/35 Codex

SCTE 104 links an Automation System to an Injector, and it defines only the upper layers of the stack, leaving the physical path open. The normative default is TCP/IP: a bi-directional, connection-oriented link modeled on SCTE 30 and expected to be reliable and low latency. There is commonly one socket per output channel, but a device that holds several Injector Instances can accept them on a single socket and route by DPI_PID_index. The same messages can instead ride inside the video signal, carried in the SDI VANC space per SMPTE ST 2010, with a return path or one way. That choice decides what is possible. A two-way link (clause 13.2) lets the Injector answer with responses and heartbeats, and redundancy is the Automation System's job: it connects to the backup Injectors it has been configured for. A one-way VANC link (clause 13.1) cannot carry responses at all, so it runs best effort and typically retransmits each message. Where the Injector physically sits is left flexible on purpose: it can be a black box inside the encoder, a separate chassis holding one or more Injector Instances, part of the multiplexer, or everything in a single chassis. A Proxy Device (clause 7.5) bridges the two worlds by accepting the API over TCP or serial and placing the resulting messages into VANC for the Injector, running the initialization handshake on its behalf. The SMPTE ST 2010 VANC carriage and the Proxy Device belong to the later editions; the original 2004 edition described in-video carriage (VANC and HANC) and analog carriage without the Proxy Device. As an engineering matter an Injector built directly into the encoder makes frame-accurate output timing easiest, but the standard is deliberately architecture neutral and several layouts are valid.