Genlock and Timecode Explained (With Signal-Flow Diagrams)

What is genlock, and what problem does it solve?

When two video sources are not timed to each other, their frames do not line up. A switcher trying to cut or dissolve between them is jumping between two unsynchronized timelines. On the take that shows up as a glitch. Or a roll. Or a flash. Genlock (generator lock) means locking a device's internal video timing to an external reference, so every source in the system starts each frame at the same instant. It removes the problem by giving everything one clock to march to.

Two cameras look fine on their own, but the moment the TD cuts between them the picture tears or hops. The classic symptom is the clean-switch failure. Not a bad camera. Two cameras running on their own timing, with nothing forcing them into step.

Genlock is the thing that forces them into step.

How reference gets distributed

Genlock is not a setting you flip on one box; it is a signal you distribute.

A reference generator (often called a sync generator or master clock) produces a timing reference, and that reference is fanned out to every device that needs to lock: cameras, switchers, servers, processors, each of them slaving its timing to the incoming reference instead of running free.

Two reference-signal types you will see named in menus and spec sheets are black burst and tri-level sync; which one a facility uses depends on the formats it runs and what its gear accepts, so match the reference type to your devices rather than assuming.

Topology is the concept that matters: one reference source, distributed to many devices, usually through a dedicated reference distribution amplifier or a managed chain of reference inputs and loop-throughs.

• A reference generator produces the master timing signal the whole system locks to.
• Distribution fans that one reference out to every device, commonly through a reference DA rather than blind daisy-chaining.
• Each device has a reference input (often labeled REF, GENLOCK, or SYNC IN) and a setting to slave to it.
• Termination on reference runs is device-specific; follow the gear and DA documentation for how each input expects to be fed or looped.

What is timecode?

Every frame gets a unique address. Timecode is a running clock expressed as hours:minutes:seconds:frames, written HH:MM:SS:FF. Where genlock answers "are these two pictures aligned in time," timecode answers "which exact frame is this," so devices can agree on a shared point in the timeline for playback sync; multicamera alignment in the edit; event logging.

Timecode is commonly carried as its own signal and distributed alongside the video reference, so devices share both a locked picture and a shared address. LTC, linear timecode, is one widely used form.

At the concept level, keep the two apart in your head. Genlock aligns the timing of the video signal; timecode labels the frames. A system can be genlocked without a shared timecode, and can share timecode without being genlocked. Many broadcast and film workflows want both.

Genlock vs timecode: why both exist

They are complementary. Not alternatives.

Reach for this table when someone on the crew says one word and means the other:

Because they travel together and both come off the sync chain, crews collapse them into one idea. Then they get surprised when a genlocked system still will not line up in the edit (no shared timecode), or a timecode-stamped system still glitches on the cut (not genlocked). Two jobs, two things to plan; both belong on your broadcast signal-flow diagrams.

Where genlock and timecode show up on a signal-flow diagram

Sync is infrastructure, and infrastructure that is not drawn is infrastructure that gets forgotten.

On a signal-flow diagram, give reference and timecode their own lane, the same way you separate the video path from the audio path. Draw the reference generator once, then draw the distribution out to every device's reference input explicitly, one line per device. Skip the vague "everything is genlocked" note in the corner.

Drawing it port-to-port turns the intention into a buildable fact: the same discipline covered in how to create an AV signal-flow diagram. Every reference and timecode run then becomes a labeled row you can hand to the crew, and it forces the question you want asked in preproduction: does every device that needs reference actually have a free reference input, and is anything on this list unable to genlock at all?

For the full picture path this sync lane sits under, see the multicamera livestream signal flow walkthrough in the broadcast signal-flow library; for the crew-facing method of documenting a signal path end to end, building your first diagram covers the mechanics.

Common sync mistakes

Most sync problems are planning problems rather than gear problems; here are the usual ones:

• Treating sync as a per-device toggle. Genlock is a system property rather than a checkbox on one camera. If the reference is not distributed to every device that needs it, the ones left out still fight the switch. Plan reference for the whole system, then confirm each device individually.
• Forgetting to distribute the reference. A reference generator sitting in the rack does nothing until its signal actually reaches every device. Draw the distribution explicitly so a missing reference run shows up on the page, not on show day.
• No plan for sources you cannot genlock. A laptop often has no reference input. Neither does a consumer camera or a remote feed. Route it straight into a switcher that expects genlocked sources and expect trouble. That is what a frame synchronizer is for.
• Assuming genlock gives you timecode, or the reverse. A locked picture is not a shared address. If the edit needs cameras lined up, plan timecode distribution too, and document it in the signal flow for crews workflow so nothing is left to assumption.

Frame sync: the fix for sources you cannot genlock

Not every source can accept a reference. Laptops, consumer cameras, streaming returns and many playback devices run on their own free timing and cannot be told to slave to your generator. A frame synchronizer (frame sync) is the concept that solves this. It takes an unsynchronized (wild) source and re-times its output to your system reference, so the switcher sees a source that behaves as if it were genlocked.

Conceptually, a frame sync buys clean switching on sources you do not control. Many switchers include frame synchronization on their inputs, and so do many converters and processors, but whether a given input re-times a wild source is a per-device fact worth confirming in the gear documentation rather than assuming. On the diagram, mark which inputs re-time wild sources so the plan is explicit about where a laptop or remote feed becomes safe to cut. The PTZ camera system design guide shows the same layering idea. Video. Control. Power. All on one drawing, which is exactly how a reference/sync lane earns its own layer.

Frequently asked questions

Is genlock the same as timecode?

No. Genlock aligns the timing of the video signal so devices can be switched cleanly; timecode is a shared time address (HH:MM:SS:FF) that labels each frame for sync and logging. They often travel together on the same sync chain, but a system can be genlocked without shared timecode and can share timecode without being genlocked. Plan and draw them as two separate things.

Do I need genlock for a single-camera livestream?

Usually not. With one video source there is nothing for it to be out of time with, so there is no switch to glitch. Genlock becomes necessary the moment a switcher has to cut, mix, key, or composite between two or more live sources. A single camera straight to an encoder rarely needs reference.

What is black burst versus tri-level sync?

Both are reference-signal types a sync generator can distribute for genlock. Which one a facility uses depends on the formats its gear runs and what each device accepts, so match the reference type to your equipment and house standard rather than to a rule of thumb. For the exact signal type, level, and termination your devices expect, follow the manufacturer documentation and your broadcast engineer.

How do I show genlock and timecode on a diagram?

Give them their own lane. Draw the reference generator once, then draw a line to every device's reference input, and draw the timecode feed alongside it, instead of writing a vague note that the system is genlocked. Drawing sync port-to-port turns it into a labeled, checkable row instead of an assumption. You can build this lane in a free WireFlow diagram.

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