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Strange movement between 2 static keyframes

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Ken EvansStrange movement between 2 static keyframes
by on Nov 2, 2011 at 5:04:32 pm

I have 4 keyframes in a very basic move on a comp.

KF 1 moves the item onto the screen. KF 2 stops it. KF 3 tells it to move again and KF 4 stops it again.

However between KF's 2 and 3 although there is no difference between them, there is a strange to and fro movement on the item. If I grab the bezier handles and twist the path it shows there is a little loop there and the item dances around it during the paused section where it shouldn't move.

I can't seem to get rid of it and I had this problem before and forgot how to solve it.

Any ideas what this is????


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Michael SzalapskiRe: Strange movement between 2 static keyframes
by on Nov 2, 2011 at 5:25:39 pm

It's called the boomerang effect and is talked about here: [link]
It even includes a link to a couple of Creative COW tutorials about it.

- The Great Szalam
(The 'Great' stands for 'Not So Great, in fact, Extremely Humble')

No trees were harmed in the creation of this message, but several thousand electrons were mildly inconvenienced.


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Roland R. KahlenbergRe: Strange movement between 2 static keyframes
by on Nov 2, 2011 at 6:24:53 pm

The solution is to set the first of the 'repeat' keyframe to a Hold KF. More folks should how and when to use it.

Aharon Rabinowitz provides a pair of video tutorials on the Creative COW website that describe the issue and solution for the boomerang motion problem that arises from unintentionally having Auto Bezier spatial interpolation set for keyframes of equal value:

The above quote is taken from the Adobe link by Michael. The text I have underlined is to highlight the issue on hand. The boomerang effect can also come about from any non-linear Spatial Interpolation. IOW, the boomerang effect is not restricted to having Spatial Auto Bezier keyframes.

Lots of folks do not appreciate how the boomerang effect is created. Unfortunately, Aaron didn't touch on this in both of his tutorials. It's fine knowing the solution to a problem but it's better to know its cause. For now, just take note that the boomerang effect is NOT caused by an anomaly in AE but by user-error.

Hopefully, I can find some time to do a tutorial. For now, should you want to Hold on to a position, ensure that you use a Hold keyframe.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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ben g ungurenRe: Strange movement between 2 static keyframes
by on Nov 3, 2011 at 4:09:40 am

FWIW, there is an AE preference to "default spacial interpolation to linear" keyframes (off by default). I prefer to turn this on, and then bezier things up on my own after roughing out the initial animation. I find I have fewer unexpected results this way.

Really, this should be the default pref in AE, as default bezier throws less-experienced users off pretty frequently. But I suppose it's been the other way for so long, it would disorient a lot of experienced users if suddenly the pref changed...

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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Roland R. KahlenbergRe: Strange movement between 2 static keyframes
by on Nov 3, 2011 at 6:48:10 am

[ben g unguren] "FWIW, there is an AE preference to "default spacial interpolation to linear" keyframes (off by default). I prefer to turn this on, and then bezier things up on my own after roughing out the initial animation."

Very true Ben. Unfortunately, from having taught hundreds of AE users in a classroom environment, it's inevitable that a Bezier-type Spatial Keyframe will be used in the course of one's work. Then, we're back to where we started.

As long as folks apply a Hold Keyframe when they want to hold onto a property's value, the boomerang effect is a non-issue.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Ken EvansRe: Strange movement between 2 static keyframes
by on Nov 3, 2011 at 10:15:50 am

Thanks very much for all the very helpful answers.

Now I understand exactly how this happened!


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