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Motion optical flow problem...

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Chris Prouse
Motion optical flow problem...
on Feb 21, 2011 at 8:18:58 am

Hi,

I'm having trouble with Apple Motion's optical flow. I'm slowing some 60p footage down to about 20% and exporting the clip as ProRes 422 LT. The exported file's slow-mo play's back really smoothly for a couple of seconds... and then it starts getting really jerky. I've tried restarting... sending the clip to motion from a 60p timeline in FCP... closing all the other open programs... importing the original file directly into motion... trying different clips... but the clip keeps coming out smooth for a few seconds and then becomes jerky for the rest of the clip. Any idea's on what's causing the optical flow to only work for a couple of seconds on my clips?

Thanks in advance for any help!


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Stephen Smith
Re: Motion optical flow problem...
on Feb 21, 2011 at 3:32:39 pm

60p. If you haven't, run it through Cinema Tools first. Change its frame rate to 24 or 30 and it will slow it down to half speed real well. Then bring it into Motion to slow down more. Hope this helps and best of luck.

Stephen Smith
Utah Video Productions

Check out my Motion Training DVD

Check out my Motion Tutorials


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Chris Prouse
Re: Motion optical flow problem...
on Feb 21, 2011 at 10:34:09 pm

I've been using optical flow on the footage first and then conforming it afterwards from 60p to 30p (though the footage becomes jerky after a few seconds even if I don't conform it afterwards).

I tried your suggestion and conformed it to 30p first, then ran it through optical flow at 40%, but the same thing happens... beautiful slow-mo for a couple of seconds and then it suddenly becomes jerky. I'm editing on a 2010 i7 MBP with 4gb of ram... which slows nearly to a halt when exporting the optical flow (paging out issue perhaps?).... do you guys think it could be a lack of ram? The exported ProRes 422 LT files coming out are 500-1000mb in size.

I should probably upgrade to 8gb of ram anyways... but I'm curious to know if you guys think this is causing the problem.

Thanks in advance for any help!


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Thomas Weimer
Re: Motion optical flow problem...
on May 2, 2011 at 7:11:30 pm

Do you see a little gray circle spinning to the left of the play head in motion. If you do then the clip is still rendering the background process. This happens automatically when you select optical flow and depending on how long your new clip will be determines the time it takes to render. I have a Intel Core Duo with 6gb of ram and it took 30 minutes to render out from a 10 second clip. Once it is completed it should play all the way through smoothly. Hope this helps.


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Kevin Keegan
Re: Motion optical flow problem...
on Jul 14, 2011 at 8:48:05 pm

I have glitchy playback as well when using this technique. During playback it will play back 10 or so frames smoothly when arrowing through it, and then one frame will pop up that is from a few frames back, and then the next frame is the next in order again. And the cycle continues.

This is on a rendered movie mind you. I've brought in the movie back to FCP both before and after the conform from 60p to 23.98 and it does this no matter what... within QT or FCP.

Thought I might be trying to go too slow with it but even a 40% reduction using optical flow caused this.

FYI my video was from a go pro where the shutter speed can't be set manually. But regardless, this shouldn't happen, the effect might not be as convincing but it shouldn't be staggering frames like that.


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