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Old December 30th, 2010, 11:08 PM   #1
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Fixing sync in a multi-cam environment

I recorded a show with 3 cameras- no time code so obviously free run.

2 of the three cameras have sync'd up perfectly- sound and video are in great shape. However for half of the show, the third camera is just a bit off- probably a half a frame or so, but there are close-ups on some of the performers and the notes and fingers in the image don't quite match up. It is consistent so it isn't a drift issue.

How do I move sync by half a frame or so? I can obviously nudge things a frame at a time, but I need to nudge it a bit less than that.

Thanks.

--Ben
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Old December 31st, 2010, 12:09 AM   #2
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You can't. The frames have to sync and you couldn't move the start of a frame to line up with the middle of a frame on another track.

But a half frame is only 1/60th of a second and you shouldn't notice that, not even in close-up.

This is why the real high end multicam pros (of which I am not one) use external timecode generators to send the exact same sync pulse to all the cams. Best I can do is use the TC LINK feature on my Z5s -- and frankly it doesn't work all that great.

Not sure what you mean by "no time code so obviously free run." Free Run is timecode, and I don't know of any digital cams that don't have some form of TC. What cams did you use?
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Old December 31st, 2010, 12:34 AM   #3
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I've had issues with tape dropout, and lost the synch myself..

What i do is go back to the nested sequence (where all your cameras are on the timeline), and razor the problem frame, and move it over to match the other clips..
Hopefully, if you've got audio coming into all the cameras, the waveforms should be a giveaway for matchup. If not, you'll need to a visualization of the matchup..(ie somebody clapping, blinking, etc....)

Basically, what i'm saying is feel free to break the problem clip and move it to synch..
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Old December 31st, 2010, 01:00 AM   #4
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Sorry- When I've done audio work on film sets- it is double system- time code sync with a slate and everything. This was basically 3 camcorders running on their own with no blackburst or anything to force them to run together at the same rate. I could get around this taking video outputs of the cameras then recording on decks that are sync'd from a master time code and blackburst, but as I digress...

3 cameras- a consumer Sony handycam, a Sony NX5U and a Canon XHA1s.

Not a dropout issue- I had that elsewhere in the project. The Canon's tape had a couple dropouts of a couple frames each. Drove me nuts going through a 2 hour concert to find those issues.

And yes- I would think that half a frame wouldn't be noticed, but in this case I can and it is driving me nuts. I'm a musician myself and this is classical music. A violinist's left hand moving quickly with rhythmic music can look wrong at 5ms out. Half a frame (rough approximate) is close to 17ms. Sometimes you don't see it as being massively out (like other sync issues), but the feeling is unsettled and it just doesn't seem to sit right.

Sometimes I wish the film/video world could work with the same precision as the audio world.

--Ben
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Old December 31st, 2010, 01:22 AM   #5
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I guess it's not much of a consolation that your clients likely won't notice the difference. An odd thing that I've noticed is that even perfectly synced audio and video can sometimes appear to be out, especially in the scenario you've described.

But with the level of cam you note above, especially three really disparate ones, it's just going to be something you have to live with. We often shoot with up to six cams and even with TC LINK, the actual waveforms don't always match up on the timeline. It's more than just a TC issue; it's physical, because the signal can vary based on when the cam moves into record mode. Each full frame -- the minimum interval you can use to sync with -- encompasses a full 1/30th of a second and that clapper spike could be anywhere in that very long interval.

I suppose 60p cams would give you twice the number of sync points or half the interval. Either that or move up a class level and use cams with genlock and external TC in. EX3, G1 or H1, etc.
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Old December 31st, 2010, 07:00 AM   #6
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Ben, you can change the timecode display to audio samples or milliseconds, among other options (several ways to change it; in the PDF Help it is on page 93, or just keyword "audio sample"). From there you can unlink the audio track from its corresponding video track and nudge the audio as little as one sample if you want, then re-link to whichever video track you want to synched to.
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Old December 31st, 2010, 11:55 AM   #7
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But then wouldn't any audio you move in this fashion be out of sync with its own corresponding video?
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Old December 31st, 2010, 01:14 PM   #8
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Pete-

I've missed that... thank you so much for the tip. That will solve a multitude of sins in future productions. May not help fix only one camera that is out, but I'll give it a try.

Adam- for me the problem often is audio coming off the DAW that I do my mixes on. Moving the audio a small amount would be fantastic when I drop the new sound into an existing sequence. As for with a single camera, it could bring things out of sync- just would have to work with it.

--Ben
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Old January 1st, 2011, 07:37 PM   #9
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you can simply slip the AUDIO into sync with the picture. although poorly documented, Prem Pro permits sample accurate editing & sliding of audio, and FCP to 1/300th of a frame.

at 24/25FPS sync can look loose. its just how it is and while you can sometimes slide the audio a bit for a better sense of sync, not always. you can simply make yourself crazy trying, maybe sliding about 1/4 of a frame will get everything closer.

also DSLR's ( 550D, 7D, 60D, 5D ) record audio 1 frame out of sync :(

TC is way too inaccurate to lock cameras together to actually lock cameras you use video sync, normally composite video, but sometimes HD tri level sync. however, most lower end camera's lack any sort of sync input.
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