So, you have a multi camera shoot and you want to have the timecode in perfect sync between all of the cameras. For a start lets assume we are talking about pro cameras that actually have timecode in and out, because without a way to connect an external timecode source, getting truly accurate TC sync is all but impossible. The other thing you need if you want REAL timecode sync is genlock (or an Arri Alexa with an Ambient Lockit box).
The most common way used to get timecode sync across multiple cameras is to simply connect a timecode source to the timecode in of the cameras. This can be done with cables or wirelessly. This is a method I’ve used many times and it works….. kind of. Actually this is NOT the best way to get good timecode sync, but it’s probably the most commonly used method. It is especially problematic when you have very long takes, say shooting a rock concert without stopping between songs.
Here’s the problem.
When you hit record on the camera the timecode MUST increment by 1 frame every time you record a new frame, regardless of what the timecode on the TC in is doing. Every frame MUST have a unique TC number. So, if the cameras sync clock is running a tiny bit faster or slower than the TC clock of the external source, the cameras TC will slowly drift out of sync with the external TC until you stop recording at which time the cameras TC will re-sync with the external TC. On long takes this may result in a loss of sync between the external TC and the TC generated by the camera. Often this isn’t more than a few frames, but on a music shoot or where you have sync sound, being a few frames out can be a real pain.
Timecode will not synchronise a camera, it will not pull the cameras frame rate into sync with the external TC clock. Unless it is an Arri Alexa and you are using an Ambient Lockit box as Ambient can pull the Alexa’s clock into sync via a special “Tune” pin. The only thing that will alter the cameras actual frame or sync rate is genlock. So if you want the cameras to truly stay in sync you must genlock them to a common sync source.
Now I know that very often this is not possible, especially with remote or mobile cameras. That’s why companies such as Ambient include a sync output that you can connect to the cameras genlock in on their wireless TC boxes, so you can genlock the camera to bring it in to true sync with the external clock as well as feeding it sync TC.
If your working with a single camera and a sound recordist, rather than having the soundie feed TC to the camera, the more accurate way is to use the camera as the TC source and send the TC to the sound recorder. The sound recorder doesn’t have a frame rate as such so the TC does not need to be in sync with the sound recorder in the same way as it should be in sync with the cameras actual frame rate. A sound recorder can have time periods shorter or longer than a frame, a video camera cannot. By sending the TC from the camera to the sound recorder you will eliminate sync drift between the TC and the actual video frame count during longer takes.
I know this is not how it’s done in practice. In most cases TC is sent to the camera and in most cases genlock isn’t used. Probably because this is the easiest way to do things. Most of the time, if the takes are shorter than 10 minutes or so, you won’t see any issues. But if you really want accurate TC over long takes you need to do it properly and either genlock the cameras or use the camera as the TC source on a single camera shoot.