Audio and Video Sync Weirdness on Macs... help.

Posted: Wed Feb 13, 2008 9:51 am

So....

For my day job, I multimedia.... Smile

We've been having a problem for a very long time now...

We record hour long lectures on our sony HDV Camera...

we also record the un-eq'd audio, for editing purposes, using Logic Express v. 7.1.1 on a Powermac tower w/ a 933 mhz G4 processor... 1 gig ram..... OS X v. 10.4.10....

the microphone interface is a maudio octane preamp into the maudio Delta 1010... w/ pci interface...

This Powermac is dedicated to capturing audio... nothing else.

Right now I'm editing on a dual 3 ghz quad-core Intel MacPro w/ 8 gigs of ram... OSX v. 10.4.11 (won't upgrade to Leopard till the bugs are gone)... But I've been on the top of the line Mac's for 5 or so years... G5's... Dual G5's... Quad G5's..... you name it... and each machine has had the problem (yet to be described).... Smile

My workflow is:

Raw HDV.... > captured directly into Final Cut Pro... > Import the 44.1 khz aif file created by Logic Express on the "Audio capturing Mac"... (16 and 24 bit... doesn't make a difference) ... then I'm prepared to work....

THE PROBLEM....

I place the video on the timeline..... then... i place the audio on the timeline.... match up the beginning frames... the audio and video fit perfectly together at the beginning of the talk...... 30 or so minutes into it, the audio has gradually shifted to being a quarter or so second off.... by the end of the talk.... the audio and video have about a second gap between them...

The problem isn't the camera... We've recorded talks for 5-6 years with multiple DV and HDV cameras.... we've always had the same problems..

The problem isn't the "audio capturing computer"... we had a G5 in there, but figured it was WAY too much overkill to have that machine in there just capturing 1, 2, 3, or even 4 audio tracks every couple of weeks or so...

The problem isn't hard drive speed... we've had multiple hard drives.... on multiple machines... no difference....

as far as we can tell... it's not hardware...

I've been to Macworld and WWDC... Talked to Apple's engineers about the problem.... nothing..... I've had the top level of apple's video support on the phone.... nothing...

no one in the entire industry seems to know what our problem is....

we've done basically everything you can think of...

The problem is really annoying... but I've been working around it for years.....

got any ideas?
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Posted: Wed Feb 13, 2008 10:50 am

Yes, I have an idea. HDV will come in audio at 48k. You say you are importing your audio at 44.1K... you should be recording your audio at 48k.
Convert your audio to 48k first before importing. OR, change your sequence audio rate to 44.1k.

Please look in your Browser (the bin) in FCP and scroll over and take a look at your media and sequence settings. Make sure the sample rates match and you are not in the 24p framerate for HDV. Regardless of what apple says, HDV should be 29.97.

Posted: Thu Feb 14, 2008 11:15 am

It can't be the difference between 44.1 and 48K. That would show up as about 5 minutes difference in a 1-hour take. It's much more likely to be the relative accuracy of the video and audio clocks, or possibly the accuracy of the sampling rate conversion algorithm in Final Cut Pro.

You would need not only to record both at the same sampling rate (e.g. 48KHz) as BRH suggested, but also lock the sampling clock of the Delta 1010 to the clock in the camera. Without more details of the actual Sony camera in use, it's difficult to say whether this is possible, or to give you specific instructions on how to do it.

Posted: Sun Feb 17, 2008 3:34 pm

Check the frame rate at which you recording the video at. If you shot at 30fps then dropped it into a FCP timeline that was at 29,97 your going to have a problem.

Or it could be the clock in the old comp is drifting. If you have any other clock source I would lock to that and try again. That is if its not the fps being off.

Posted: Sun Feb 17, 2008 7:44 pm

We tape a lot of concerts that last upwards of 1.5 hours.

We are lucky in that they are never done strait to DVD and are always edited so we can move the audio a bit if it does not line up. At the end of a 1.5 hour concert we are off about .5 seconds.

Maybe you could do the same and nudge the audio a bit in the middle of the show when editing.

I think for-a-song is probably correct and it is a difference between the frame rates. A good way to check this is to record time code on the camera and on the video recorder and see how much they are off at .5 hours and 1 hour.

Best of luck!

Posted: Tue Feb 19, 2008 4:03 pm

I'm with -TOM-

a long record with seperate clocks and at different smple rates
I'd expect there to be some time trouble

I'd basically do what Tom is saying
but
I'd record the audio at 48k with m-Powered cos I''ve had trouble with Logic let alone Logic Express
just being biased from bad thing a very very long time ago

then import both into your video editor FCP
I would set the audio track as my time line
then have a couple of video lines
the video track would be copped into smaller sections and bumped to get lip sync

where there is gaps you can use frames to stretch or use larger sections from elsewhere just to give the impression or a second camera

I know that means more edit time
but it is a technique that could lead to a better look and once you have the method it can be a quick edit once you get your fingers programmed

don't tell anyone about this cos it's been one of my little secrets that has impressed on many an edit for live concerts
even better when you add some graphics and styled overlays ... slo mo's etc ... fake strobes and stutters ... in those gaps
you can do this mid song too but then the edit time really grows

Posted: Tue Mar 04, 2008 6:05 pm

Yup, I bet its the frame rate. I work alot with audio for Film and Video and you have to be very careful on the import, making sure all the stats stay the same as when you recorded it.

timecode is a great thing or if you do not have the means for it, use a slate and do a beginning and tail slate on every shoot.

If the frame rate is the problem, you can do a pullup or pulldown of the audio, usually at .01% unless the frame rate difference is much greater than the 30 to 29.97 for instance 24 to 30 which also happens quite a bit.

Good luck.

Posted: Tue Mar 04, 2008 6:16 pm

Some lecture that would be...

He walks in the door, bangs a clapboard (technical, yes), rambles on for 20 minutes about networking, bangs it again, rambles on for another 20 minutes, bangs it once more and just for safety's sake, claps it for the final time before leaving the class.

Posted: Fri Mar 07, 2008 2:14 pm

I was not being specific too just his lecture, my comment was ment as just something you should do in the situations that alow.

anyway, good luck and hope you figure it out.

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