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Freaky double framerate problem - 25fps footage plays at 50fps

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Francois Stark
Freaky double framerate problem - 25fps footage plays at 50fps
on May 18, 2010 at 12:50:54 pm

Hi

I captured hours of footage from a DVCPRO HD tape deck (1080i 25 PSF) into Apple Prores (HQ) 1080i 50. The footage has a weird problem:

When I play it back in quicktime, the info window reports the file's framerate at 25 fps, but it plays the video back at 50fps. This playback error happens acros multiple systems in QT 7.6 and QT x (snow leopard).

I open the files in FCP, and throw one on a new timeline, and accept the settings that it applies to the timeline - 1920 x 1080, square, upper field first, Apple prores (HQ), timebase 25 fps. And with these settings, on this timeline, it plays back the file right. Perfect. 25fps.

But I have no way of getting it to standard def. Because if I throw the clip on a PALtimeline (DV, Prores, Prores (HQ) - whatever), it has a green bar and needs to render. AND IT RENDERS THE FOOTAGE in 50FPS! everything plays double speed and goes out of sync since the audio is not affected. Audio plays at the right speed everywhere.

At this moment it seems my only way forward is to play the footage out of this system over HDSDI and recapture it on another system in another codec, and test it. DVCPRO HD codec...

Weird, don't you agree? Anybody seen this problem before? I run a studio where we capture 1080i 25 direct to apple Prores on Kona cards and have never seen this problem before.

The system I captured on is a brand new Mac Pro 4core, with Decklink Studio card, os X 10.5.8 and FCP 6.0.5. We tested playback on several systems (leopard, snow leopard, G5 and Intel) and they all play back the same way - so it has something to do with the captured files.

Thanks
Francois







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Francois Stark
could it be PSF?
on May 19, 2010 at 6:24:35 am

Update:

I did some more tests on these clips: When I have the clips on a native Prores (HQ) timeline, it plays right, at 25 FPS. If I add a color corrector, it will play the color corrector back at 25 FPS in real time, as long as it is not rendered. As soon as I render the timeline, it renders at 50 FPS.

Outside FCP, in quicktime the weirdness continues. The file indicates 25fps, but if you step through it using the right arrow, while watching the TC counter, you see that you step twice for every frame count increment. And you see two new frames on the image for every frame count increment. Very weird.

So the solution was this: We did not have the DVCPRO HD deck anymore and we needed the footage. We connected two FCP suites together, running HDSDI from one to the other. Played out the freaky clips from one suite and captured into the other. Back into the same codec. Apple Prores. Problem gone, except that we could not use deck control, so our newly captured clips' timecode is wrong.

The only cause I can think of could be the PSF frame structure of the video coming in from the DVCPRO HD deck. This could be causing the decklink driver to be cofused: The capture setting is 1080 50i, but the incoming video is 25psf... which uses a interlaced frame to show progressive images... mmmmm

Francois


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Kristian Lam
Re: could it be PSF?
on May 19, 2010 at 7:44:12 am

Hi Francois,

I would like to have a look at one of the captured file if that's possible. Can you forward me a link to download it via support@blackmagic-design.com?

Thanks


regards

Kristian Lam
Blackmagic Design


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Francois Stark
File...
on May 19, 2010 at 9:35:22 am

The smallest file captured with the problem is 16GB.

I will have to do some tests. I have exported sections from the timeline, which exhibits the same fault. But I think what happens is that FCP renders the clip at double speed in 25FPS, "baking in" the problem at 25FPS without actually playing at 50fps, like the original captured files do...

The best I can do is to try to re-create the problem on Monday when I get the DVCPRO HD deck again, capture a short clip and post that to you.

Regards
Francois



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Kristian Lam
Re: File...
on May 19, 2010 at 12:11:06 pm

Hi,

If that's not too much trouble, it will help us trouble shoot the issue.
thanks


regards

Kristian Lam
Blackmagic Design


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Francois Stark
Re: File...
on May 26, 2010 at 7:51:29 am

Unfortunately I could not reproduce the problem. I connected the same deck, used the same capture settings. This time the files captured perfectly - no playback or render issues.

But wait, I just realised something. Maybe the footage was shot in interlaced this time, not PSF... I did not check.

I'm getting the deck again for a last time. Will check.
Regards
Francois

Regards
Francois


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