Today, we have a guest post by James Nighswonger of Over Easy Audio on Timecode. Timecode can be a confusing and often misunderstood component of the filmmaking process, so having a detailed guide like this from an industry professional like James is fantastic.
With that short introduction, here’s an Complete Guide to Timecode.
Terminology of various forms of synchronization
There are three types of sync:
This is used to synchronize multiple video sources’ field rates to be in phase with each other.
This is used to synchronize multiple digital audio sources’ sample rates to be in phase with each other.
This is used to synchronize multiple devices and media (both audio and video) on a metadata level.
Genlock (generator locking) is most often simply called ‘sync’, it’s even labeled as such on lockit boxes. If someone uses the word sync to mean timecode, that is technically incorrect. It is a common mistake though and you’ll look like a jerk correcting everyone.
An important thing to note is that genlock is only important during live feeds, such as for television broadcast. Any time you need to combine two or more videos sources into one. You do not need to worry about genlock in post, because software will automatically align the frames of all footage.
Unless you’re working in high end sound production, you do not need to worry about wordclock either. The only time you’d see them on set is if there’s more than one recorder and wanted to make sure their clocks were completely in phase with each other. It is a feature included in some lockit boxes, though, so it’s good to know what it is.
For most production gigs the only synchronization you need to worry about is timecode.
For more information about an overview of how genlock works and specifically how it’s different from timecode this article explains it easily.
How timecode works
Wikipedia states: “A timecode is a sequence of numeric codes generated at regular intervals by a timing synchronization system.”
We’re actually working specifically with SMPTE timecode. SMPTE just stands for Society of Motion Picture and Television Engineers, the people who created the standard. It’s assumed that you’ll always be working with this protocol so it’s not needed to clarify it.
You’ve probably seen by now what a timecode counter looks like. It’s in this format:
2 Hours:1 Minute:59 Seconds:29 Frames
The hours portion can also be used as a 24 hour clock. So 14:01:59:29 is 2:01 PM. Most timecode will be used in 24hr free run mode.
(Small note if you see a semicolon next to the frames like this 02:01:59;29 your frame rate is using drop frames.)
There are two main types of SMPTE timecode: LTC and VITC.
“Linear timecode, a.k.a. “longitudinal timecode” and “LTC”: suitable to be recorded on an audio channel, or by audio wires. To read LTC, the recording must be moving, meaning that LTC is useless when the recording is stationary or nearly stationary.
Vertical interval timecode, a.k.a. VITC (pronounced “vit-see”): recorded directly into the VBI (vertical blanking interval) of the video signal on each frame of video. The advantage of VITC is that, since it is a part of the playback video, it can be read when the tape is stationary.”
In short LTC is an audio based signal, VITC is part of the video signal.
Most often you’ll be dealing with LTC, even with a video camera that has a specific timecode input.
This is probably because the downside to LTC, the fact that is has to be moving to be read, stopped mattering much when everything went digital. So now it’s just easier to send out audio signals for timecode.
Just so you have the knowledge, this is what LTC timecode sounds like:
So if you ever hear that in post, that means mute that audio channel and tell your editor to read it as timecode.
Timecode signal and work flow on a film set
The goal of timecode is to synchronize all the cameras and audio recorders on set so that in post it’s a matter of clicks to sync them all up correctly.
Timecode is a metadata level form of synchronization, meaning it does not affect how the source devices are actually recording their medium. The timecode on a digital file can always be changed to something else later if need be, unlike a film’s frame rate.
So we need to get timecode into every device and have them all running the same exact timecode. There are three ways a device can maintain/record timecode information.
- A timecode generator that (obviously) generates its own timecode. No external devices needed.
- A timecode reader that takes a continuous external timecode signal and inputs it into the device.
- An audio recorder that simply records an audio LTC signal.
A single device may have all three of these options, and even a DSLR can record timecode through its mic input.
If a device does not have its own TC generator, or contains an unreliable one, then it cannot maintain timecode without being constantly connected to an external clock.
As with all forms of synchronization there needs to be a master device designated for all other devices (slaves) to follow. So technically you only need one actual generator to synchronize every device on a film set.
This is not too common, though, because then every single slave would have to be constantly connected to the master either via wire or wireless. For static shots this may not be a problem, but for shoots where the camera is moving, it can be troublesome.
The solution is for a device to have both a reader/generator and jam sync to the master. This means connecting the master device and a slave only for a moment, so that the slave can sync to the master’s clock.
Once the slave has synchronized, the master is disconnected and the slave switches to using its own generator. So now both the master and the slave are running separately on their own generators but in sync with each other.
This sounds like the ideal solution: devices do not have to be connected and sync is maintained. World isn’t perfect like that, so there is a problem with this setup.
Since both devices are using different generators, over time the slave will begin to drift from the master clock. The quality of the generator will determine the amount of drift that occurs. A high quality generator will boast that it will drift 1/2 – 1 frame over 24 hours, but such accuracy comes with an expensive price tag.
For normal drift problems, most professionals will compensate by doing a jam sync once at the beginning of the day and once at lunch. Also make sure to jam sync after any frame rate changes, such as changing to/from a slo-mo shot.
A huge thing to note:
Cameras rarely are left to use their own generator because many are of poor quality and are unreliable. Some cameras will even turn off their TC generator mere minutes after the camera powers off, stopping the TC from running.
This means that when you turn it back on again the timecode will be way off from all the other devices. Always verify the reliability of a generator before depending on it.
To maintain the camera’s independent movement, the solution is to use a dedicated TC box, often called a lockit box, attached to the camera that provides a continuous timecode input for it. These devices use high quality generators that will continue to run timecode for the camera regardless if the camera powers off.
Because of the unreliability of camera TC generators, dedicated lockit boxes are often mandatory.
Arri cameras are the only exception, being the only manufacturer to include a high quality generator within the camera. You should still verify their drift amount during a workflow test.
Example workflow setup
You have a camera, an audio recorder, and a smart slate that all need synchronized timecode.
• For optimal results plan a workflow test before the first day of production. Better to find the problems and fix them while an entire crew isn’t on the payroll.
• Choose your master clock device. Pick a device that has a reliable clock and is convenient to bring around the set to jam sync the other devices with. Often the audio recorder will be the master, or at least the audio recorder’s lockit box.
• Select the correct frame rate on all TC devices.
• Set clocks to run 24hr free-run mode. This mode has it constantly running in relation to the time of day. Other modes will only run the timecode when recording, which isn’t much use for our purposes.
• Figure out which devices will run on jam sync, and which will need a maintained connection.
• Connect the TC output of the audio recorder into the TC input of the cameras or their lockit boxes. Different cameras may have different inputs.
Some use a BNC cable, some others use a special LEMO cable. Sometimes it’s just an audio jack. Always make sure you bring the right adaptors/cables.
• Set the camera/lockit box to jam sync/reader mode and wait for it to start running the exact same code as the audio recorder.
Use your eyes to verify that they are indeed synchronized, but be careful doing this as some camera displays will have delays. A good thing to test for in the workflow test. **
• Disconnect the cable and let the device run on its own, verify again its maintaining sync.
• The smart slate may need a dedicated cable from the audio recorder. Simply connect the cable and you should see the reader display the correct timecode.
… and that’s it. Super simple once you know what you’re doing. Sometimes cabling, faulty generators, and specific equipment quirks can cause problems so again, always try to do a workflow test before production day.
Example gear used for timecode on film sets
Ambient makes some of the best timecode devices on the market. They provide everything needed and have a custom network protocol that sync all their devices wirelessly (ACN), removing the need to jam sync.
It includes loads of metadata+software that usually the scripty or DIT would have to manually write. They are quality products and their prices reflect that.
Take to see all their timecode products.
They have three lockit boxes. A Master Lockit, Lockit Sync Box, and Tiny Lockit. To utilize all the features that their ACN network protocol provides you need at least one of the Master Lockit devices.
You’ll have to go on to see all the stuff the ACN provides, but it’s a lot and pretty useful.
If you only want them as normal lockit boxes, then you can probably just buy their Tiny Lockits. They’re the same as the Lockit Sync Box, but they don’t have a sync port (sync meaning genlock here, as stated earlier).
Largely unnecessary, unless you’re summing video signals for live work. Though if you’re going with this route you may want to think about buying a box from Denecke instead.
Denecke’s products are a bit cheaper if you only want a jam sync box with none of the extras.
Using all my above info though you should now be able to read about all the feature differences between products and know what you’re getting.
One last thing I’ll note is a new product that came out recently, funded by an Indiegogo campaign. It’s called Tentacle Sync.
It’s the cheapest solution on the market right now and the generator’s reliability has been tested to be great. They also are physically the smallest boxes, so sticking them on a camera won’t be as big a hassle for the camera op as other boxes. You control their settings via a laptop or app on the phone.
Literally, the only complaint I’ve heard about them is they don’t have a locking connector for the timecode, it’s an audio jack with right angle connector cables.
For most situations it’s really not a problem ever, and I’ve heard people using a bongo tie to strap it down, so it’s nearly impossible for anyone to accidentally unplug it. Something to be aware of though.
They’re crazy cheap, though, so worth looking at.
To compare the cost of timecode vs. audio sync (sending an audio feed from the audio recorder to camera, and then using PluralEyes to sync in post), usually the cost difference was so crazy that the demand for timecode decreased when Pluraleyes’ automatic audio sync proved to be effective.
Thing is, I often have to send a wireless hop of the signal over to camera because they don’t want the physical tether of the XLR cable. I use the $630 Sennheiser G3 wireless system to do that, and it’s prone to dropouts and batteries dying. A Tentacle Sync box, even two, is cheaper and more reliable than sending a cheap wireless hop.
I hope you’re found this article covering the different issues and processes involved in timecode enlightening. If you have questions, thoughts or comments about what you’ve read here, let us know in the comments below. And don’t forget to share this post using the share buttons right below.