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Varicam recording audio 2 frames out of sync
We’ve come across something rather odd. I’ve gone through the tapes from the field frame by frame and it’s become clear that the audio is out of sync–two frames early, to be exact. It’s clear that the sync problem is on the actual tape, this is not a Final Cut Pro issue. We’re shooting at 23.98, and this seems to be an intermittent problem. Our immediate solution is to fix it in post, since the footage has already been captured (with 1200A’s via firewire), by sliding the audio tracks two frames forward. If this is an engineering problem within the camera, then we need to send it out for evaluation. Has anyone come across this before? Any recommendations?
Thanks
Luke -
15 Replies
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How did you determine that the camera was recording out of sync?
I’m particularly skeptical that the camera could randomly vary in and out of sync.
I suggest that you shoot a clap-board for reference, then adjust the offset in your NLE.
Best regards,
Leo
Director/Cinematographer
Southeast USA -
[Leo Ticheli] “I’m particularly skeptical that the camera could randomly vary in and out of sync.”
I’m with Leo on this one, Even thought you say it is on the master tapes My guess is something else was happening on during capture Was the audio split on capture or were you routing the audio and video from separate sources or were you working with embedded audio from the camera.
Gary Adcock
Studio37
HD and Film Consultation
Chicago, IL USA -
I’m suprised that Leo doesn’t know about this!
The Varicam does record the audio two frames early; this is because the compression carried out on the picture requires so much number crunching and therefore time.
The correct workflow is to ignore this offset until you’re completed editing and then make the two frame correction.
The new “H” model provides an option to put the sound in dead sync, but this does create potential problems when mixing footage with “V” or “F” models, be forewarned. The menu setting is in the VTR page!
JS
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Hi John,
We prefer to set an offset at the time of ingest. Then you have perfect sync throughout the edit process.
Good shooting!
Leo
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[john sharaf] “The Varicam does record the audio two frames early; this is because the compression carried out on the picture requires so much number crunching and therefore time.”
DOH!
even I had a brain cramp on this one John.
This is the very reason that apple is having an issue with the 720p HDSDI capture in FCP.Gary Adcock
Studio37
HD and Film Consultation
Chicago, IL USA -
Leo,
So, of course you knew about the two frame offset!
Because in my shop we’re editing long form documentaries, where we often add materials as we go along, we leave the origional offset throughout, so that there there is consistancy!
Others must make an informed decision about when to correct the sync; but be aware that at some point it must be done!
Regards,
JS
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All,
I’m going to chime in on this one. Virtually all digital camcorders have a sync difference varying from 1 to 3 frames either advanced or delayed. Usually the video is delayed. Those folks who have been shooting digital for a while are quite aware of this issue. Notice what happens with DV.
What it basically boils down to is that any time a digital signal is processed, it takes time, usually a delay. This is inherent in every manufacturer’s equipment, not just the Panasonic VariCam.
Now you may ask why isn’t this taken care of in the camera when the recording is made? Quite simply, various processing requires different times to process the video. Keeping track of this variation as it relates to audio would be a huge electronic task which might even require an additional board in the camcorder, thus making the camera larger and increase the weight, not to mention the additional battery power. So a compromise was made.
As has been stated by Gary and John, this is usually taken care of in Post. It is a known issue and folks have been dealing with it for years, at least since digital came on the scene.
In a perfect world, this issue wouldn’t exist. But we have it and we know how to deal with it.
Good shooting and editing.
Jeff Merritt
Product Line Business Manager
High Definition Products
Panasonic Broadcast
323-436-3676 -
Jeff,
Your reply begs the question; how are you able to provide dead sync in the “H” camera without the extra board and power issues?
JS
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This is why FCP has offset control. As I mentioned, we prefer to set this in FCP as material is ingested, then you are working with material in perfect sync through out the edit.
When the picture and rough audio are cut, we generally send a Quick Time to the Audio Suite for sweetening and music mixing. The audio Engineer returns the finished audio file which simply replaces the original audio tracks.
Best regards,
Leo
Director/Cinematographer
Southeast USA -
Jeff,
The issue of audio delay has been with us for quite longer than we know.
Even standard def betacam CCD camcorders had the problem. The reason we did not see it as much as we would in high def is the lower resolution in standard def “masked” the issue to some extent.FYI Sony’s F900 is one frame out of sync in terms of audio to video.
A common technique in the field for me is to use a Rane audio delay to compensate during the original audio recording in the field. However this is not so easy when doing simple ENG crash and burn style shooting.
The use of digital audio delays are quite common on multicamera truck operations.
Tony Salgado
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