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capture offset difficulty

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cmlundy
capture offset difficulty
on Jan 15, 2007 at 9:39:57 pm

Here's the situation. Capturing 525 23.98 (DV/8bit/10bit..whatever) via Kona 3. I work at a post facility and have done this with several tapes and decks. The source is 1080psf 23.98 on either HDCAM or D5. The signal is routed to the Kona 3 and it downconverts to 525 23.98. Get the settings right and it's wonderful. No playing around with pulldown or anything 29.97. Capture is fine, looks nice etc. Here's the problem: timecode of the captured clip is off by 1 frame. If my IN point was 01:00:00:00 then I get a clip that starts at 00:59:59:23.And no changes to the capture offset can get the clip to match the tape. I have tried all numbers within reason and most have no effect at all. Our normal setup includes a -1.5 offset and I can capture from the same tape to full 1080psf 23.98 and the TC is dead on accurate to what is on the tape. Then I switch my settings so the card downconverts to 525 23.98 and voila, timecode is off by 1 frame. For now my workaround is to Modify the timecode in Final Cut and then the client gets and accurate Quicktime. Any thoughts on why this might be happening? Something about the conversion that's messing up the card slightly? I have a message in to AJA right now but thought I'd post for thoughts?

G5 Quad 2.5Ghz/4.5 GB RAM/ 10.4.8/ Kona 3 ver. 3.3 /

Chris Lundy


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David Battistella
Re: capture offset difficulty
on Jan 15, 2007 at 10:40:37 pm



I wonder.

The workaround might be to set the capture to -2.0 or 2.5 (not ideal, i know)

This must have something to do with the pulldown order in the downconvert and how the time is being calculated. It should be recieveing the same TC signal, but maybe final cut is doing something because it is an SD source. It might even be the round number at the start time. what if you made the in 00:59:59:23? What happens then.

Also this could be a drop non drop issue as all 23.98 material is generally NON drop frame.

David



Peace and Love :)


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Leigh Jewell
Re: capture offset difficulty
on Jan 15, 2007 at 11:45:41 pm

This may sound very strange... but, are you doing a video only capture? I have noticed for HDCams (I think) that I have to capture with audio even if the tape is MOS. If I do a video only capture, I have the same problem and nothing I do in the capture presets make a difference. If I do a video and audio capture, everything is dead on. I'm using a Kona2 and haven't done that particular flavor of capture, but if you are doing a video only capture, that's my guess.

Leigh


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cmlundy
Re: capture offset difficulty
on Jan 16, 2007 at 12:36:43 am

I am capturing video and audio. I have also tried the -2.5 offset and even tried -5 and -10. The latter 2 usually result in capturing at the wrong IN and OUT point completely, but the difference in the captured clip and the tape was still 1 frame. BTW, my HDCAM tape in recent tests has TC burn-in so I can keep track of what's going on more easily.

Don't know about the non-drop frame issue. For capture you don't choose drop or non-drop in settings anyway. You get what the deck is giving via 422 and in this case it's all non-drop.

This process should be easiest because it's only a scaling issue. The frame rate should be untouched. Maybe there's an issue AJA isn't aware of.


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JeremyG
Re: capture offset difficulty
on Jan 16, 2007 at 5:02:54 am

I think the 1 frame delay is standard with a downconvert. it's not really 'only a scale'. There's frame interpolation (pulldown) to be added and that combined with a scale could slow down everything by a frame.

Are you sure you are using the capture offset correctly?


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cmlundy
Re: capture offset difficulty
on Jan 16, 2007 at 2:33:07 pm

Well, I'm pretty sure I'm using the capture offset correctly. When I capture everything else on these systems we need a -1.5 offset. I'm talking HD, SD, everything. Like I said, I can capture from the same tape and deck at 1080psf 23.98 with no timecode issue. Also, there's no pulldown being done by the card for this conversion, it is only scaling. The input is 1080psf 23.98 and the frame buffer is 525 23.98 with the downconvert. The frame rate is untouched, and 29.97 never rears its ugly head. I'm hoping for an answer or some recognition of a problem from AJA, as I have a message in to someone in tech support. But if any has any other thoughts I'm all ears.


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JeremyG
Re: capture offset difficulty
on Jan 16, 2007 at 2:37:07 pm

When you create the new device control preset, do you select it in the device control preset tab before capturing?

Jeremy


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cmlundy
Re: capture offset difficulty
on Jan 16, 2007 at 5:17:40 pm

Not sure what you mean. But I select a device control preset that I've created for Panasonic or Sony at 23.98 and has a -1.5 capture offset. I then change it to something new for each capture test. This works correctly when not downconverting the 1080psf signal so the device control is theoretically fine.

The capture preset is where the 525 downconvert comes in. You basically edit an existing one to have the compressor of your choice, with 23.98 frame rate and an Input source of 525 23.98 (not 29.97).


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JeremyG
Re: capture offset difficulty
on Jan 16, 2007 at 6:45:01 pm

Yep, you are doing it correctly. Has AJA weighed in yet?


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R.Howard
Re: capture offset difficulty
on Jan 16, 2007 at 7:04:52 pm

Chris,

We are not seeing this issue on our end with the AJA hardware itself. We have seen issues of frame offsets due to latency in items such as routers, other applications and decks.(we built in a method of dealing with that) and although it's not often an issue, it is out there. Not sure if your going thru any gear that could be the culprit but it may be worth a try.

I'm guessing your using FCP by the G5.

The hardware is solid, sometimes it's just everything else in the mix that screws things up. I would like to also note the AJA hardware is running under Linux with our own app and driver. I know users are Mac based here and I try to only chime in when hardware seems to be the question. Hopefully to give you a different perspective of how the same item can work entirely different under different circumstances to help narrow down your issues.

Best of Luck,
Ramona

Ramona Howard
SpectSoft, LLC
593 Hi-Tech Parkway Suite B
Oakdale, CA 95361
Phone: 209.847.7812 extension 104
Fax: 209.847.7859
http://www.spectsoft.com

RaveHD - Changing the way you think about HD


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