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Keyframe Velocity

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Mohammed SultanKeyframe Velocity
by on Jul 9, 2010 at 2:28:51 pm

Why is keyframe velocity in After Effects measured in pixels/sec? I thought it would be frames/sec (it`s name even has "frame" in it) !


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Dave LaRondeRe: Keyframe Velocity
by on Jul 9, 2010 at 2:50:54 pm

Velocity is expressed as a ratio, as in 25 kph. Every hour, you move 25 kilometers.

Keyframe velocity does NOT refer to changes in the keyframe.

It's also a ratio, and it refers to the difference in a property over a defined amount of time. So for the position property, a layer's velocity can be 750 pixels/sec.

If you use Bezier keyframes on the position propery, you will note that the velocity changes from frame to frame as AE speds up and slows down the layer.



[Mohammed Sultan] "I thought it would be frames/sec"

Think about it: that's a measure of TIME as expressed by a ratio, and not a measure of VELOCITY.



Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Mohammed SultanRe: Keyframe Velocity
by on Jul 9, 2010 at 7:11:06 pm

It's also a ratio, and it refers to the difference in a property over a defined amount of time. So for the position property, a layer's velocity can be 750 pixels/sec.

So, what would it mean for a layer`s velocity to be 750 pixels/sec?

I see the Timeline, and I want to make a change in a property, say, for 2 seconds (and get the property back to what it was before these 2 seconds,) what should I do?

Thank you,


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Dave LaRondeRe: Keyframe Velocity
by on Jul 9, 2010 at 7:26:08 pm

[Mohammed Sultan] "So, what would it mean for a layer`s velocity to be 750 pixels/sec?"

In PAL, it means that a layer moves 30 pixels each frame. Depending on whether this motion is x-y axis only, z-axis only or a combination of all three, it can appear to be moving at different speeds.

In NTSC, it means that a layer moves slightly more than 25 pixels each frame. The actual distance is 25.02502502503 pixels/sec, due to NTSC's 29.97 frame rate.

To be honest, I don't think I've worried about a layer's velocity more than twice in my 17 years as an AE user. I go by what I see on the screen.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Kevin CampRe: Keyframe Velocity
by on Jul 9, 2010 at 7:31:05 pm

so you have keyframe at position1 and a keyframe at position2....

if you want the layer to return to position1, select that keyframe and choose edit>copy. move the cti to the position2 keyframe, then hit 'page down' to move one frame further and then choose edit>paste.

you should now have three keyframes, the first and the last should be the same position, so the layer should move from position1 to position2, then immediately move back to position1 on the next frame.

i don't think you really need to be concerned about velocity for this, unless you are trying something that i am missing....

Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW


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