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Strange Effect in After Effects - with simple keyframe motion

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Eric Holzapfel
Strange Effect in After Effects - with simple keyframe motion
on May 4, 2009 at 4:28:31 pm

Hello Creative Cow forum,

I have been playing around with After Effects CS4 (a trial copy) on
a Windows XP machine. I created a PSD image in photoshop that is
853 px wide and 1706px high. My idea being to do a vertical pan
on the image in After Effects. I created an AE comp that is DV 16:9
widescreen. I set a position keyframe at the "bottom" of the image, at about 426,250 (or whatever the values are), and at the end of the pan, set a keyframe at the end of the comp (comp is 10 sec long) at the top of the image. So my pan goes from the bottom to the top.
About half-way through the pan I would like to stop and hold a constant y position for a second or so, and then continue to pan up. I put two keyframes at the y postion that have the same value (370). The x position does not need to change. My problem is that as the pan comes to the first 370 keyframe and passes to the second 370 keyframe, the image jumps up and down a few pixels between these two keyframes.
I did not try to render the comp, I am just previewing it. Is it me or Windows XP?


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Todd Kopriva
Re: Strange Effect in After Effects - with simple keyframe motion
on May 4, 2009 at 4:35:28 pm

The spatial interpolation mode for your keyframes is Auto Bezier (the default). You can change the behavior that you're seeing by setting the spatial interpolation mode for these keyframes to Linear.

Some people call the motion that you're seeing 'boomerang' motion.

See "Spatial interpolation and the motion path" for more information, including links to some good videos here on the COW about this issue.

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Todd Kopriva, Adobe Systems Incorporated
putting the 'T' back in 'RTFM' : After Effects Help on the Web
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