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Timecode vs Sync — Key Concepts

BOTH

Timecode and sync are often confused, but they serve completely different purposes on a motion control shoot. Understanding the distinction is essential for achieving frame-accurate repeat passes, and for understanding why timecode alone is not sufficient.

What is Sync?

Sync (synchronisation) is a pulse generated by the camera each time it takes a frame. It is an output from the camera — not an input. When this pulse arrives at Flair, Flair locks its move timing to the camera's actual frame timing.

This is what makes repeat moco passes frame-accurate. The camera is "wild" by nature — it takes its own time to expose each frame. Sync tells Flair exactly when each frame occurred so the rig's position data is locked to the camera, not to an independent clock.

Film cameras generated sync mechanically. Modern digital video cameras generate it electronically as a clock pulse. MRMC Flair hardware can read sync pulses at framerates up to approximately 800 fps.

What is Genlock?

When a camera has no sync output, the solution is to feed it a genlock signal — a studio-wide timing reference that tells the camera exactly when to take each frame. The genlock is usually generated by a dedicated device such as an AJA Gen10. The same signal can simultaneously be fed to the camera, to monitors in the studio, and to the Flair hardware as a sync input.

The only real advantage of taking sync directly from the camera (rather than genlock) is that the camera can run at any framerate — including unusual rates like 800 fps or fractional rates — whereas genlock devices typically only generate standard broadcast framerates (24, 25, 30, etc.).

What is Timecode?

Timecode is a continuous clock that counts hours, minutes, seconds, and frames from a set starting point. It is used to identify when a take starts and ends, and to synchronise a music video move to a soundtrack.

Timecode does not lock the camera to an exact moment to expose each frame. It tells you what time something happened, not that the camera shutter fired at exactly the right instant.

"Flair can trigger from timecode but CANNOT frame accurately synch to it." — Simon Wakley

Timecode can be used as a reliable trigger point — to fire Flair at a precise moment in a music track, for example — but it does not replace sync for achieving frame-accurate pass registration. Both are needed for a music video shoot: sync for frame accuracy, timecode for triggering to the soundtrack.

Digital camera jitter

Modern digital cameras generate their sync signal from a divided-down crystal clock. Some rounding up and rounding down occurs in this division, resulting in jitter in the sync signal. This was not a problem with mechanical film camera sync (which varied only slowly, if at all).

With slower moco rigs, this jitter was too small to matter. However, fast rigs (such as the Bolt) can respond to this jitter. A smoothly running rig can become rough and shaky when locked to a jittery sync signal.

One Shot Sync is the solution: lock to only one pulse at the start of the move rather than continuously. This works if both the camera and rig are running at exactly the same framerate. The first pulse of some cameras can itself be slightly wobbly, so this is not always perfect — but it mostly works in practice.

The booplight and frame 1

A booplight (flash) can be used to tell the editor exactly where frame 1 occurs in a multi-pass moco shoot. It should be triggered after the camera has ramped up to correct speed, since most modern digital cameras have a variable delay before the first frame is actually taken.

Timecode input into Flair

There are three ways to get timecode into Flair:

  1. LTC In port on the RT14 — 3.5mm mini jack stereo (TRS) connector. This is the most common method.
  2. Serial port — requires a special device.
  3. UDP — requires a special protocol.

If the Serial/External device for timecode is set to a serial port that does not exist on the system, Flair will fall back to the RT unit automatically.

Source: The difference between timecode and sync — accuracy of passes — talk.mrmoco.com