Shift keyframe with an expression?

[Robert]

Hi all,

I made a camera follow a path with the basic shelf tool. This means it keyframes your current start and end frame and applies an ease int/out effect. Is it possible to shift the end keyframe with an expression to make the animation length customizable while still keeping the curve and make it stretch to fit the new frame range?

[woodenduck]

If I understand you correctly, what you are looking for is the smooth expression function.

Put the following in to the position parameter of the object following the path, it will automatically adjust so that the start and end point of the animation corresponds to the first and last frame of the scene's frame range.

smooth($F, $RFSTART, $RFEND)

[Robert]

Thanks for the response,

In the most basic situation (eas in/out) this would be the perfect solution. However, I want to control the speed of the camera along the path and the most basic way to do this would be to change the slope of the curve between keyframes and maybe even add new ones in between. Is this correct way to approach it or is there a way to get more control over the speed along the path without using keyframes?

[edward]

What about creating two channels. The first one, you keyframe as usual. The second channel (that is on the position parameter), references the first one using chf() using some modified version of the time so that it stretches out the first channel into the required length of ($OT - $IT).

[edward]

An alternative is to use chop() in your position parameter to reference a CHOP track. Then you can do keyframing (Channel CHOP) and then a Shift CHOP to stretch it out.

[Robert]

Thanks for the answer,

The solution with a secondary channel and using the chf() expression to reference it works very well.