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Old June 16th, 2011, 11:29 AM   #1
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How important is Syncing 2 cams via BNC

I have a Canon XF305 and was getting ready to order an XF300 when I realized they can not be synced via bnc cable. I originally purchased the XF305 because I could not find an XF300.

Now I hate to get cheap if syncing multiple cameras is a great benefit.

So how important is syncing cameras before post.

I edit with premier CS 5 so some of the syncing software does not work.
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Old June 16th, 2011, 11:37 AM   #2
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Re: How important is Syncing 2 cams via BNC

Denny, I assume you're saying that your cameras can be genlocked. If so that is the industry standard method for synchronising cameras and should be encouraged. If memory serves me correctly I think you'll need to jam the time code from one camera also.

In fairness though, unless you're doing a great deal of multicam work, the modern NLE methods for syncing up clips using sound waveforms or Pluraleyes have their own devotees and I'm not sure that these days I'd let the ability to genlock cameras be the over-riding consideration when purchasing.
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Old June 16th, 2011, 12:47 PM   #3
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Re: How important is Syncing 2 cams via BNC

Are you using FCP? That can sync via manually determined in points. You can easily select these from a definite (sudden) audio or visual cue. Time code sync is easier but not essential and can stray over longer time periods. Genlock isn't critical for non-live 2D.

Nice to have, not critical.
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Old June 16th, 2011, 12:56 PM   #4
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Re: How important is Syncing 2 cams via BNC

I do a lot of 3 to 5 hour multicamera shoots and it seems like the most
important thing is to figure out which of the cameras drop frames and
under what workflow conditions frames can be dropped or added.

The actual free-run accuracy between identical cameras is fairly good even
without genlock. It is easy to loose a frame here or there in post with the
modern cameras that split video into 2GB files etc.
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Old June 16th, 2011, 01:41 PM   #5
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Re: How important is Syncing 2 cams via BNC

When I sync via audio waveform, I keep in mind that when everything lines up perfectly, it's not truly synced. Since sound waves travel slower than light, a camera mic further away (like at the back of a church) will be a few frames delayed compared to a camera mic up in front of the church where I am. Therefore, the best way to sync multiple cameras is timecode or a visual cue like a flash.
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Old June 16th, 2011, 02:51 PM   #6
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Re: How important is Syncing 2 cams via BNC

Warren, with great respect, surely syncing with timecode or flash will produce exactly the same lack of offset as syncing by waveform? The only way to overcome the phenomenon (and you're quite right it does exist) is to make the correction in post before you start editing.

The problem is that an offset of, say, four frames - 1/6th of a second - might well be observed as a mismatch in vision.

Since our rear-of-church camera never gives us BCU of the celebrant, our practice is to ignore any audio offset and know that when the priest raises his hand for the blessing it'll happen at exactly the same moment on all shots. Not ideal but our chosen compromise.
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Old June 16th, 2011, 03:15 PM   #7
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Re: How important is Syncing 2 cams via BNC

Quote:
Originally Posted by Philip Howells View Post
Since our rear-of-church camera never gives us BCU of the celebrant, our practice is to ignore any audio offset and know that when the priest raises his hand for the blessing it'll happen at exactly the same moment on all shots. Not ideal but our chosen compromise.
This is actually how I sync everything up, usually 3 cameras and at least 2 other audio tracks. Just eyeing up and then making small adjustments from there, nothing too technical or involved. It doesn't matter if it's "true" sync -- you just have to make it believable.
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Old June 16th, 2011, 04:47 PM   #8
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Re: How important is Syncing 2 cams via BNC

All good discussion. I'm not a wedding shooter but do a lot of marching band and other musical events for local schools and such. I am specifically spending the extra money for the XF105 and XF305 rather than 100/300 for the timecode synch, and possibly genlock in case I run into contract work hooking into someone else's live-switching environment.

I've had to manually synch multiple cameras in post many times in the past and it can be a hassle, especially when working with inexperienced shooters who aren't good at making sure there are good synch events in the leaders. I'm expecting that even if they go untethered, having the same free run time code on all cameras will free my operators to start and stop recording as they see fit without giving me pains in post.
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Old June 16th, 2011, 09:18 PM   #9
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Re: How important is Syncing 2 cams via BNC

Quote:
Originally Posted by Philip Howells View Post
Warren, with great respect, surely syncing with timecode or flash will produce exactly the same lack of offset as syncing by waveform?
Imagine a two camera shoot of a marching band's half time show. One camera is down on the field shooting closeups, the other is recording wide shots from the top of the stadium. Both are recording audio from it's on-camera mic. If you sync up both waveforms perfectly in post, the image of the wide shot will always lag behind, and will get worse the further the camera is from the subject.
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Old June 16th, 2011, 10:23 PM   #10
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Re: How important is Syncing 2 cams via BNC

Thanks guys, I went ahead and went with the XF305 so when I do use two cams its just easier to sync. This was my biggest chore and figure I have half the equation mine as well get the second half and make it easier.
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Old June 17th, 2011, 12:23 AM   #11
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Re: How important is Syncing 2 cams via BNC

Quote:
Originally Posted by Warren Kawamoto View Post
Imagine a two camera shoot of a marching band's half time show. One camera is down on the field shooting closeups, the other is recording wide shots from the top of the stadium. Both are recording audio from it's on-camera mic. If you sync up both waveforms perfectly in post, the image of the wide shot will always lag behind, and will get worse the further the camera is from the subject.
Warren, I don't think we're disagreeing, just expressing things with different words. The problem as I understand it it that, to use your example, assuming you want to use both soundtracks - ie the far camera is recording its audio from a radio mic up close to the audio source (which is what happens a lot with multicam weddings), either the audio or the vision is going to be out of sync,
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Old June 18th, 2011, 10:56 PM   #12
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Re: How important is Syncing 2 cams via BNC

Depends on your set-up and workflow.

For me, running several hundred feet of cable to sync cameras is much more of a hassle than taking two minutes to sync them in post.
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Old June 18th, 2011, 11:43 PM   #13
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Re: How important is Syncing 2 cams via BNC

Well, yes and no.

First off, you do not have to have everything permanently cabled-together to set and maintain sync. You can cable your multiple -cams, get them rolling and the t/c locked, then you unhook the cable and move the cameras into position. As long as you don't turn anything off, the timecodes stay (pretty much) in sync.

I also sometimes use external audio recording devices, as well, and for them, there is no choice but Plural Eyes and/or wave-form matching. You do have to be careful to pick the camera with audio pickup from the stage/altar/whatever to synch to.

Otherwise, I'm with Warren on this in that I think still camera flashes are the easiest way and best to find and maintain sync for multi-cam shoots of weddings and events. I've used Plural Eyes and manual matching of wave-forms but find that those methods work best when you have the audio pick-ups all in more or less the same plane, as Warren and Philip have noted. I shoot weddings and events with as many as seven cameras. Only a few of my cameras have the capability for time code sync. So, even if I were to lock the timecodes together, I would still have to rely on a camera flash for the other units.

For long programs, I do check the synch periodically because clocks can drift relative to each other. A drift of even a couple of frames of video can be noticeable.
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