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Old August 12th, 2010, 09:01 PM   #1
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AV sync: audio lags in Cineform RAW?

OK, capturing in Cineform RAW by SI-2K camera.

1080p29.97; CFHD RAW Quality 3; audio input via USB interface (fantastic quality RME Fireface).

With clips under 2min length, all is good.

If the clip is over two minutes, then between 2m and 2m30s you can see how audio starts lagging vs image, so sync goes out of the window.

First I thought the sync issue was playback-related. However all players, and Premiere CS5, do show the same AV sync issue.

I even re-encoded the file to High HD setting in post, and sync problem is still there.

So it happened at the acquisition stage.

I measured 7 frames audio lag at 3min 30sec mark - a very large sync issue there already.

Question: is this a known issue with SI-2K capture?

What is the root of the problem, in your opinion?
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Old August 12th, 2010, 09:42 PM   #2
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It is a question for SI. Tim Bucklin shot a SI-2K for 48 Hour Film Project a few weeks ago, and it mark the files as 24.0 when he was sure it was set up as 23.976. That will throw off the audio.
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Old August 13th, 2010, 10:20 AM   #3
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Correction: problematic recording was made at 1080p30, not 1080p29.97 as per my post.

In any case, SI2K seems to correctly mark the file 30p, as it should.

I have a hunch that this may have something todo with either the digital clock (both video and audio are being input digitally...), or audio buffer overflowing.... Just speculating here. SiliconDVR's memory indicator is always showing only 2-4% memory utilization, so should be good on that front...

I have made 5min and 8min recordings since, one 1080p23.98 another 1080p29.97 (actually, not 30p) - and both have perfect audio sync.

This worries me a lot because I was unable to reproduce the problem... thus it may pop at any time again.

Will try 30p test today.

SI2K is sensitive to USB bus, I'm afraid there could be issues there. If you have any other suggestions - they are most welcome...
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Old August 13th, 2010, 09:33 PM   #4
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After many tests... I think the conclusion is, my SSD data drive was having issues.

Replaced with a regular 2.5" HDD, works great now - no more AV sync issues.
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Old August 15th, 2010, 03:22 PM   #5
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SSD drives work well until they have filled up all empty space for the first time. The industry's solution to this is called TRIM. The drive manufacturers usually supply a TRIM utility with the drive, which must be run periodically to clean up the drive. This support is integrated into Windows 7, but isn't in XP.
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Old August 15th, 2010, 03:27 PM   #6
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I thought this was OS-specific?

If not, will Win 7 (which is what I have here) run TRIM automatically on a removable drive that happened to be SSD?
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Old August 21st, 2010, 07:56 PM   #7
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TRIM support is supposed to be integrated into Win7, but I haven't had any experience with it to make sure it works properly. I'd check the SSD manufacturer's website to see what they recommend doing on Win7.
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Old September 10th, 2010, 08:49 AM   #8
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is there a freeware application to check the TRIM on a windows XP SSD drive? My toshiba portege m750 has a SSD drive that I record to. It would like to test this drive out to make sure it won't have any future problems.
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Old October 5th, 2010, 06:07 PM   #9
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Quote:
Originally Posted by David Newman View Post
It is a question for SI. Tim Bucklin shot a SI-2K for 48 Hour Film Project a few weeks ago, and it mark the files as 24.0 when he was sure it was set up as 23.976. That will throw off the audio.
David, there is an option when creating a new project to "Conform" your project. This overrides the true frame rate and forces your player to always use the selected "Conform" frame rate when playing back.

Its been the cause of many headaches in my world. Not only does it affect audio, but it effects the pace that the files play back at as well.

SI3D new project menu | http://www.flickr.com/photos/52426934@N04/5055139327/

lets see if i can attach a screen shot.... nope... link instead...
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