Global Slow-mo effect - Animating Time scale

Question

Is there a way to animate the timescale of a scene for a small amount of time? I'm looking to create an animation, and in the middle it goes from 1.0x speed, to 0.125x speed (1/8th normal speed), but with a smooth transition. So it's start at 1.0x speed, and over the course of 10 frames, for example, it slows down to 0.125x speed for a bit, then goes back to normal speed.

Ideally, I'd just keyframe the time-remapping to do it, but apparently it's not animate-able.

Going into the action editor and changing the scale of the clips won't be viable, as it's important that the whole scene is slowed down (nearly everything in the scene is in motion, so slowing down the main subject won't cut it). So it needs to affect the scene globally.

I've also seen solutions that say to do it in the VSE on another scene with an effect strip (i.e. using the main scene in the VSE as a source, and then attaching an effect strip to it), but it doesn't seem to have any effect on anything when I go back to the main scene. Which kind of makes it pointless as a solution, as you can't iterate on it unless you render, and re-render it after a tweak.

I'd rather not have to render out that section with 8x the frame rate and slow it down in post if I can help it, as that seems rather wasteful.

I'm also sure this could be done easily with animation nodes. But as this is a project with a strict deadline, I can't set aside the time to learn the addon's ins and outs at the moment.

Answer 1

You can do it in the graph editor. Select all elements in the scene and place a locrot keyframe where you want the remapping to start. In the graph editor place the cursor on that frame and select all keyframes only to the right of the cursor. Change pivot point to 2d cursor and scale on x by 8 (s-x-8). Go to where you want the mapping to end and place another keyframe on all elements in the scene, place the cursor on that frame, then select all only to the right and scale on x by 0.125 (s-x-0.125). You then only need to finesse the handles on these keyframes to give you the lead in/lead out you're looking for. Much easier if the scene can jump straight to slo-mo because you can just set handle type to vector for those two frame numbers.

edit: video link https://youtu.be/lxdQogx6y40

Answer 2

You can edit the length of an animation by using the NLA Editor.

Open up the NLA Editor and you will greeted with something like this:

We'll need to push this action down into its own NLA strip. Click the button here to push it down:

Now we can split up the strips into smaller Actions and edit these actions to be longer or shorter.

First split the strip from the frame you want to start the slo-motion effect by clicking on the strip and Right-clicking and choosing "Split Strips". (HOTKEY = Y)

Now you can slide the strips along the timeline. (Click and drag) If you click on a strip and press "Tab", a strip becomes editable.

You can scale the strip with "S" from the playhead.

Now, making sure that the current NLA track is solo'ed (the star icon) and that it contributes to the animation (the tick check box), your animation will have been slowed between the specific frames you needed.

If you need to make further changes on each strip, you can click on one of the strips in the NLA editor and press tab and make changes to it that way.

Ctrl+A will apply the scale of the strip you scaled earlier if you're happy with it.

It's often an overlooked solution to scaling keyframes from the playhead straight inside the timeline (which can often cause curves to go a bit wild) but I would recommend doing this after you've completed the animation to a point where you're happy with it at normal speed.

Hope this way can help achieve what it is you want to do.