Playback Systems
Definition
A playback system triggers media cues at the planned moment, identically at every performance. Content is organised in ordered cue lists (cue stacks) that an operator triggers by hand or that run automatically against a clock. Repeatability is the purpose of the system: a cue has to behave the same way in rehearsal and in the show.
The guide
When cues have to stay locked to other departments, synchronisation usually relies on timecode. SMPTE ST 12-1 timecode labels each frame in hours, minutes, seconds and frames, written HH:MM:SS:FF. It is distributed either as LTC (linear timecode), an audio-frequency signal carried on a cable, or as MTC (MIDI timecode), which sends the time over MIDI in quarter-frame messages, four per frame. When video playback, sound and lighting follow one timecode master, a complex sequence stays frame-accurate across the whole production.
Automation of this kind fails in full view of the audience: a missed trigger, a timecode dropout or a stalled media file is immediately visible. Professional playback systems therefore keep a manual fallback within reach, usually a GO control and a known safe state, so that an operator can take over a cue as soon as the automation fails.
The rule
Every automated cue has a manual fallback that an operator can trigger at once.
Glossary terms
Sources
- SMPTE, Understanding Standards: Time Code (ST 12-1, format heures:minutes:secondes:images) · smpte.org
- SMPTE ST 12-1 (GlobalSpec) : Time and Control Code · standards.globalspec.com
- MIDI timecode (Wikipédia, pointeur secondaire) : messages de quart d'image, quatre par image, valeur complète toutes les deux images · en.wikipedia.org
- ETC, How SMPTE works : timecode et déclenchement des conduites lumière · blog.etcconnect.com