Keyframes, and Motion

I am working on an animation where you (the camera) are in a moving car (or in a helicopter, following the car) and you are moving pretty fast.

I built a low-poly world in which you start out in a forest, then a modern city, then back in the forest. In other words, a city in the middle of nowhere.

Using 2 location keyframes, the camera starts moving after 5 seconds and stops 5 seconds before the end.

When I render it, the camera seems to “speed up” at the beginning, and then “slow down” at the end. Why does it do that?

My question IS NOT “how do I fix it?”. That’s easy.

My question IS “why does it happen?”.

(And…, are other keyframe animations (like character movements) speeding up and slowing down - and I never realized it? (Dang.))


Sorry, cant help, but maybe one of the @moderators can help ya by moving this over to so you get the proper attention.

Thanks so much. Standing by…

1 Like

Relative to what frame of reference? What’s the constant velocity thing that it’s speeding up and slowing down relative to?

Why are fcurve autohandles the default? Because they’re smoother than vector handles. And most artists prefer smooth to jerky. You can set your handles to vector handles, but then you have a noticeable discontinuity in velocity between frames 0 and 1.

Why is default extrapolation (for fcurve handles) constant rather than linear? Because there’s no such thing as linear for your first keyframe-- linear requires two points-- and you might as well keep it consistent.

Got it! Thanks.

I switched to linear and saw the expected result.

Hi bandages.

So, on this part of my question…

I use MakeHuman characters and Carnegie Mellon University (CMU) .BVH motion files a lot. I can’t wait to try them with f-curves set linear. Will it be horrible?


Probably not, because they’re probably mocap animations that are sampled at 30hz.

Agreed… a lot of the mocap data I’ve seen isn’t interpolated at all. Each frame of movement is actually captured and keyed. So chances are good you won’t see much difference when changing the interpolation values.

Yep. Y’all are correct.

Since, basically, every frame is a key frame (for every bone), and the deltas are so small - there simply isn’t enough time.

Apparently the MakeHuman/MakeWalk mocap loader code sets the fcurve to linear. I tried messing with it, but there was no noticeable difference.

Any way, thank you so much for taking the time to teach me something that after 6 years I hadn’t noticed.


1 Like


Please see reply to Fweeb …