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50p at 50% speed, judders in 25p timeline

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Luke Ogden
50p at 50% speed, judders in 25p timeline
on Aug 31, 2016 at 4:54:33 pm

Hi all,

I've been scratching my head all day on this one. It's a workflow that I've done many times before successfully, but for some reason wont work this time.

-Acquisition media is 1080 50p XAVC-S from the a7s
-Brought into an 1080 25p FCPX timeline
-Retimed to 50% in the speed editor
-Voilá! smooth slow motion and a clip twice as long (ripple is left on in this instance)

only in this project the slow motion looks terrible, the clip duration is doubled but going though it frame by frame confirms that the video frame only changes once every two frame advances in the timeline (right arrow ).

The inspector on the clip confirms that FCPX reads it as 50p, and the project frame rate is definitely 25p and Rate Conform & Automatic Speed both yield the same result. What gives?! I've done this many times before with no hitch so any input would be greatly appreciated.

Thanks
Luke

27" iMac 3.4 GHz Intel Core i7, 16GB 1333 MHz DDR3, OS X 10.9.1 //
Adobe CC Suite


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Noah Kadner
Re: 50p at 50% speed, judders in 25p timeline
on Aug 31, 2016 at 7:23:52 pm

Did you try with optical flow retiming? Slowing footage down that much can reveal the limitations of the original photography- ie if a very slow shutter was used etc.

Noah

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Russ Carlin
Re: 50p at 50% speed, judders in 25p timeline
on Sep 1, 2016 at 11:24:25 am

Did you conform the clip down to 25fps or just slow it by 50%?


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Luke Ogden
Re: 50p at 50% speed, judders in 25p timeline
on Sep 2, 2016 at 7:22:44 am

Initially I just slowed it down 50%, when I didn't get the results I wanted I looked into the rate conform options but nothing helped there.

The footage is 50p
The only thing I can think of is that a very low shutter was used in some of it. But I should still be able to see those frames right? albeit with more motion blur than usual.

27" iMac 3.4 GHz Intel Core i7, 16GB 1333 MHz DDR3, OS X 10.9.1 //
Adobe CC Suite


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Bret Williams
Re: 50p at 50% speed, judders in 25p timeline
on Sep 2, 2016 at 3:36:25 am

Did you confirm that it actually is 50p? It very well might be 25p recorded at 50p. GoPros for example will do this if there's not enough light to pull off a fast enough shutter for 50p.

_______________________________________________________________________
http://BretFX.com Plugins & Templates for FCP X Editors & Motion Graphics Artists


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Luke Ogden
Re: 50p at 50% speed, judders in 25p timeline
on Sep 14, 2016 at 9:45:50 am

Opening the file in QuickTime and bringing up the inspector indicates 50p also, one possible culprit is that I recorded at a shutter of 1/30th, less than should technically possible at 50fps, this was to reduce flicker on some screens in the scene. Is it possible the shutter speed setting overrides the format frame rate?

27" iMac 3.4 GHz Intel Core i7, 16GB 1333 MHz DDR3, OS X 10.9.1 //
Adobe CC Suite


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