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# Inertial Bounce / Time Remapping

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 Inertial Bounce / Time Remapping on May 26, 2013 at 3:35:32 pm

Hi Guys,

i have a problem concerning time remapping and the inertial bounce expression.

I basically filmed a 360° rotation of a laptop infront of a green screen and made a seemless loop from it.
I now linked the time remapping to an expression slider to have better control over rotating the laptop.

Then i keyframed a basic rotation and added the following expression (found here: http://www.graymachine.com/2010/04/my-top-expressions/)

amp = .1;
freq = 1;
decay = 2;
n = 0;
if (numKeys > 0){
n = nearestKey(time).index;
if (key(n).time > time){
n--;
}}
if (n == 0){ t = 0;
}else{
t = time - key(n).time;
}
if (n > 0){
v = velocityAtTime(key(n).time - thisComp.frameDuration/10);
value + v*amp*Math.sin(freq*t*2*Math.PI)/Math.exp(decay*t);
}else{value}

I now run into the problem that the image, when the expression comes to rest is somehow laggy, probably because of not having not enough information from the time remapped scene (it was filmed with 25 frames/sec).

Does anybody have an idea how to fix that?

Cheers

 Re: Inertial Bounce / Time Remappingon May 27, 2013 at 7:29:12 am

re-shoot at a higher frame rate - that's the only thing that will work as it should. You could try Twixtor, Time Remap, or any other similar plugin to create in-between frames but it won't be the same.

Tudor "Ted" Jelescu
Senior VFX Artist

 Re: Inertial Bounce / Time Remappingon May 27, 2013 at 2:36:47 pm

He doesn't necessarely need a higher frame rate, just a longer 360º spin.

I would try twixtor first though.

 Re: Inertial Bounce / Time Remappingon May 28, 2013 at 9:48:18 am

That is true, however not knowing what is used to spin the object I would use a higher frame rate - it will make the spin smoother.

Tudor "Ted" Jelescu
Senior VFX Artist

 Setting keyframes in Twixtor in AE CCon Feb 4, 2014 at 1:50:46 am

I'm having a problem controlling the keyframes aligned with my footage in Twixtor using After Effects CC. I'll try to describe the problem,

Lets say i put a key frame at the first frame of a shot and want it to be 100% speed. Then at say frame 125 I put another key frame and want the footage to increase in speed over the course of getting there, up to 400%. And then I want to put another keyframe at frame 135 and want the footage to return to 100% by then. What happens is, as soon as i enter the value of 400%, the footage that i see in the monitor window is now shorter; it's sped up, but the keyframes have remained where they are. What I'm finding in playback is that the footage is speeding up to 400 gradually but it never reaches that 3rd keyframe to slow, because the shot is over by then. And I'm seeing that it never actually reaches 400% either for the same reason. If the keyframes moved with the footage as it grew and shrank, then I could control how it plays out, but the keyframes stay where they were in alignment with the original speed. If I look at the effected footage as to where a certain action takes place now, AFTER I've entered 400% at frame 125, and see that it's not slowing down at the point I want it to (between original frames of 125 and 135), if I try to add the keyframes according to what I'm seeing on the monitor, the footage continues to move and I can never control where the slow down is supposed to take place. It's like the moving shell game.

Can you tell me what I'm doing wrong? Can't it be that the length of the shot in the timeline remains visually consistent and the software adjust accordingly to the speed changes? Or conversely, couldn't the keyframes move along with the footage if the footage is speeding up to react to the adjusted speed settings, so I can' still see where that speed change is taking place?

What I'm finding is that if I put in the speed change (to 400%) at frame 125 aligning with a certain action on screen, that action moves in the monitor. If I then go to where I want the slow down to take place, according to monitor showing the effected speed change, I end up putting my 'slow down' key frame BEFORE it even reaches the 400%. Also, I'm finding that, as the footage contracts in my sequence upon entering the value of 400% at frame 125, and that keyframe remains where it originally was, aligned with the original position of frame 125, the software seems to think that it should just continue to speed up to the point of that keyframe, only now that 400% keyframe is aligned with frame 200, because the footage has contracted, but the keyframe hasn't moved to stay with the action that originally took place at frame 125.

This is a very hard thing to describe but I'm sure if you're familiar with the program, you may be able to understand my ramblings. I very much hope so, because I'm keen to buy this program but can't get around this problem.

I'm used to doing time re-mapping in AE, which is ok, but not as good as Twixtor, but in AE time re-mapping, those keyframes stay with their action spot, so you're stretching or contracting time in accordance to what are essentially handles that anchor moments in time. This is why I'm having so much trouble trying to figure out how to make this work with Twixtor.