Timecode and Show Synchronisation

Every device must agree on the frame rate, such as 24, 25, 29.97 or 30 frames per second, and on the counting mode. Drop-frame counting is used at 29.97 frames per second: it skips frame numbers 00 and 01 at the start of each minute except every tenth minute, so that the timecode stays in step with the clock. Non-drop timecode at the same rate falls 3.6 seconds behind the clock every hour, which is also the gap that opens between a device counting drop-frame and one counting non-drop.

Genlock is the related technique for video. Every video device is locked to a common reference, black burst (bi-level sync) in standard definition or tri-level sync in high definition, so that their frames start at the same instant and switching between sources stays clean. Timecode sets when a cue happens, genlock aligns the frames themselves, and a large show often needs both.

Timecode gives repeatability at the cost of flexibility, because the clock does not wait for applause or a held moment. Hybrid shows therefore run timecode for the locked musical or video sequences and hand control back to a live caller for sections that follow the performers. One device is designated as the timecode master and the others chase it, since two devices generating timecode for the same system give conflicting positions.