Thu May 16, 2019 3:59 am
No, the reference input is only for a genlock/synchronization signal from something like the Blackmagic Sync Generator. This reference signal is an analog video signal (for HD video tri-level sync is usually used), that is used to time the start of a frame across different devices. The reference signal is just a pulse, it carries no time information (no numbers) and every pulse is exactly the same. But this pulse is sufficient to make sure each device starts its frame at exactly the same instant.
So if you had multiple cameras that you need to capture frames at exactly the same instant, you might use a sync generator (sometimes also called genlock) and feed the signal to each camera. This is essential when shooting 3D video with two cameras so that the left and right camera capture at exactly the same instant. It's also very important for 360 VR applications involving multiple cameras for similar reasons.
Without a reference sync signal sent to each camera, the individual frames from each camera may be off from each other by a few milliseconds in time. For a multi-camera shoot where you just cut between different camera angles, this usually doesn't matter much, because the cut itself hides any sub-frame timing differences. You'd really only notice this when viewing frames from different cameras simultaneously (which is why a sync generator is important for 3D and VR applications).
Timecode is really just a counter, it tells you what time a particular frame was captured. A timecode counter can start at an arbitrary time (like 00:00:00 in record-run applications), or it can be set to the current time (time-of-day) as a clock. Timecode is also different type of signal than reference/sync signals. Timecode comes in different formats, but as a dedicated input connector, usually LTC timecode is expected which is an analog audio signal. In the case of LTC timecode, the analog audio signal is actually used to encode what is essentially digital information, namely the numbers representing the current time/frame count.
Timecode can be used to match up frames captured from roughly the same time from different cameras, and can be used to match a video frame with the audio samples captured at the same time. So if a timecode signal is fed to multiple cameras (or video recorders) and an external audio recorder, each device can mark the content being recorded with the corresponding time stamps to assist with this.
Keep in mind that with timecode alone (without a sync reference), the frames marked with the same timecode from different sources will all be from slightly different moments in time if you were to compare them side by side. But since the differences will be less than 1 frame (less than 33ms if shooting 30 fps), for many applications this is good enough.
We should probably add an item to the FAQ for the difference between timecode and sync reference signals, as this is a frequent source of confusion.