Videomaker – Learn video production and editing, camera reviews › Forums › General › Video and Film Discussion › Questions about Sync, SDI, and Genlock
- June 10, 2013 at 9:04 AM #66017
I'm trying to wrap my head around some sync issues.
In audio, if you have two digital recorders running for any length of time, if their clocks are not locked to a single source there will be a certain amount of drift that occurs between them.
So I wonder: if you have multiple digital video cameras running, but they are not locked up somehow, will there be a similar "drift" over time?
Which leads me to another round of questions:
Say you have a camera with an SDI out, but no Genlock in (e.g. the Sony EX-1). Let's say you wanted to record two of these cameras to a central source (like a Pix 240).
Can you record the two independent SDI streams to this single box without worrying about the fact that the cameras are not referencing a central sync source? Or do they both have to be receiving Genlock for this to work?
Different, but related scenario:
Let's say you are using one camera with SDI out, but no Genlock in, and another camera that has both SDI out and Genlock in (say a Sony EX-1 and a Canon XF-105).
Is it possible to somehow derive Genlock from the SDI signal coming from the EX-1, so that the XF-105 could be in sync?
By extension, if this is possible, is there a box that could get Genlock from this SDI signal and turn it into word clock for a double-system audio rig?
I'm new to the whole video thing, so forgive my ignorance if this is not remotely possible. In the audio world, there actually is a way to do this sort of thing, so I am hoping that there is a similar workaround in video.
If you're not shooting video for broadcast, you generally souldn't have to worry about this. All you'll need to do is make sure your video is the same frame rate. Secondly, make sure the timecode for both is set to either "drop frame" or "non drop frame," and make sure all video sources are the same. If they're different, you'll get that drift. Here's a video talking about the difference between the two:
So drift between cameras is not an issue so long as the frame rates are set correctly.
What of clock drift from the double-system audio? Since that's referencing samples per second and not frames per second, I imagine there would be some loss of sync over the course of an hour.
Is there a way to derive sync from an SDI signal? Methinks if I could get genlock from this and turn it around to word clock, I'd be able to have my audio be sample-accurate with the video.
I've never had a problem with drift as long as the audio is captured along with the video in camera. If you are using external audio recorders, that's a different story.
Browse Markertek.com. They have a whole lotta little boxes . . .
I guess the Ambient Lockit is sort-of the device I am looking for:
Looks like it creates some sort of wireless network and can output genlock or word.