Playback Systems
A playback system exists to fire media cues at exactly the right moment, every single time. Content is organised into ordered cue stacks, which an operator triggers by hand or which run automatically against a clock. Repeatability is the whole point of the exercise: the same cue has to land identically in rehearsal and in the show, because anything that drifts will eventually drift at the worst possible moment.
When cues need to stay locked to other departments, synchronisation usually rides on timecode. SMPTE ST 12 timecode counts hours, minutes, seconds, and frames — written as HH:MM:SS:FF — and it is distributed either as LTC, an audio-like signal on a cable, or as MTC, carried over MIDI. Lock the video playback, the audio, and the lighting all to one shared timecode and a complex sequence stays frame-accurate across the whole production, every element chasing the same master clock.
Automation like this is powerful, but it is also brittle in a very public way. A missed trigger, a dropped frame of timecode, or a media file that stalls is instantly visible to the entire audience. That is why a professional playback setup always keeps a manual fallback close to hand — a simple "go" button and a known safe state — so that a human can step in and recover a cue the instant the automation stumbles.
Always have a manual fallback for every cue.