Jerky slow motion from Final Cut at DVinfo.net

Greg Quinn · February 18th, 2007, 01:00 PM

I'm trying to create slow motion in post with Final cut by reducing the speed of a clip - but when it's rendered to DVD, the motion looks terribly jerky - can anyone provide some pointers how I can create effective slow motion in post on FCP?

thanks.

Boyd Ostroff · February 18th, 2007, 01:13 PM

I guess it depends on just how much you want to slow things down, I've had pretty good luck in the past myself. Try it both with and without frame blending enabled. It may also help if you add motion blur. But the basic problem is that you only have 30 frames per second to work with (actually 60 fields per second) so the old cliche of "garbage in, garbage out" applies. There are some specialized applications which are supposed to do a better job; Twixtor comes to mind although I've never used it.

Also, what shutter speed did you use when you shot the footage? In my experience, 1/60 second works best if you plan to slow it down in post. If you used a high shutter speed then you're going to get jerky results because there's a bigger time gap between when each frame was captured. In other words, shooting at 1/60 second means the shutter stays open for the full duration of each video field, and you get motion blur to correspond with that. But if you used a 1/500 second shutter speed, then you would capture a sharp image of a moving subject during the first .002 second of the frame. Then you wait for .031 seconds before capturing the next image. During that time the object will be in a completely different position with no motion blur to connect it with the previous position, hence a "jerky" type of motion.

Greg Quinn · February 18th, 2007, 01:18 PM

Thanks Boyd, I'll check into frame blending.

February 18th, 2007, 01:00 PM	#1
Greg Quinn Major Player Join Date: Oct 2006 Location: San Diego, California Posts: 505	Jerky slow motion from Final Cut I'm trying to create slow motion in post with Final cut by reducing the speed of a clip - but when it's rendered to DVD, the motion looks terribly jerky - can anyone provide some pointers how I can create effective slow motion in post on FCP? thanks.

February 18th, 2007, 01:13 PM	#2
Boyd Ostroff Wrangler Join Date: Dec 2002 Location: Mays Landing, NJ Posts: 11,800	I guess it depends on just how much you want to slow things down, I've had pretty good luck in the past myself. Try it both with and without frame blending enabled. It may also help if you add motion blur. But the basic problem is that you only have 30 frames per second to work with (actually 60 fields per second) so the old cliche of "garbage in, garbage out" applies. There are some specialized applications which are supposed to do a better job; Twixtor comes to mind although I've never used it. Also, what shutter speed did you use when you shot the footage? In my experience, 1/60 second works best if you plan to slow it down in post. If you used a high shutter speed then you're going to get jerky results because there's a bigger time gap between when each frame was captured. In other words, shooting at 1/60 second means the shutter stays open for the full duration of each video field, and you get motion blur to correspond with that. But if you used a 1/500 second shutter speed, then you would capture a sharp image of a moving subject during the first .002 second of the frame. Then you wait for .031 seconds before capturing the next image. During that time the object will be in a completely different position with no motion blur to connect it with the previous position, hence a "jerky" type of motion.

February 18th, 2007, 01:18 PM	#3
Greg Quinn Major Player Join Date: Oct 2006 Location: San Diego, California Posts: 505	Thanks Boyd, I'll check into frame blending.