Timeline - new keyframes affects the previous

lzh35925

Hi,

I created a scene and saved keyframes on frame 1 on a timeline. Then I move to the next frame on a timeline, moved objects, changed poses of genesis 8 figures (significantly) on a scene and created a new keyframe. All good until frame 4 (or I just noticed the biggest changes on this frame), where frame 4 somehow started to affecting frame 3 poses.. when I create frame 4, then I change frame 3, its affects also frame 4, I can understand that, but I can't really understand, why frame 4 affects frame 3?! it's a previous frame which is already set, it shouldn't be affected by a new one. Pls someone explain to me, why new created keyframes on the newest frame affects the previous one and how can I beware of this mysterious behavior of a timeline?

Richard Haseltine

Are yuou setting keys for all proeprties in each frame, or are you just using the auto-key for those you adjust? In the latter case anything you din't set a key for will shift, depending on the type of interpolation, when the proeprty is keyed in a later frame.

Togire

Timeline is mainly for animations and tries to mimic realworld behavior. In real world, if you move, say, a hand from point A to point B, initially the speed at A is null and first the motion will be slow, then it accelerates and by the end there is a slow down to stop at point B.

In 3D, it is modelled by means of TCB interpolation. You can have details and a small visual demo here https://wiki.synfig.org/TCB

Now assume that instead of stopping at point B, you decide to add another frame after reaching point B to another further point C. Initailly, the TCB was planned for a deceleration to reach B with a null speed, but now, with the new C target the motion is different and the fact that you add a new frame to reach C, will modifie the behavior in B and this is what you noticed.

This behavior is interesting to model physical movement, but it can be annoying as, as you mentionned, frames are somehow intercorrelated. So you have the possibility to chose a diffrent behavior in the timeline: constant (the value do not change until a new keyframe is reached), or linear where intermediate frames are just interpolated in a linear way.

You just need to select the frame(s) and you can set the kind of interpolation that you want (but default is always TCB), and if you select constant or linear you will avoid that a newly created frame influence previous frames.

lzh35925

Richard Haseltine: I don't set manually those keys, they set when I change something in the scene.. although, I tried to do it manually, set transitions and rotations at least, but it didn't helped..

alainmerigot: many thx for your explanation, finally it makes sense, because when I set next keyframe and I tweek some poses, after a while the pose from previous frame is going to it's original place or at least very close to it's original place. When I changed all keyframes to linear, all the poses on every keyframe were automatically set to it's original states. So, the issue was fixed, thank you very much!

edit: in the end, I ended up with constant. Linear slightly changed the poses as I tweak new frame more and more. Constant kept them where they supposed to be..