How can I condense an animation into fewer frames, thereby speeding it up?

Question

I have a scene with a large number of objects, each with a looping animation. Most of them have the exact same animation, and it loops through 21 frames. I have other figures I want to add, also with looping animations, but these animations are different, and have a different number of frames. For instance, I have a one-off figure with a 31-frame looping animation.

I need to alter the 31-frame animated object so that its animation is sped up and condensed to fit in exactly 21 frames, so it will complete its loop in precisely 21 frames to match the rest of the objects in the scene. How do I do this?

Answer 1

Select the object, open the Dope Sheet, switch it ot Action Editor mode, select the action you want to speed up, click on the Push Down button, the action will disappear from the editor, it is still available in the dropdown panel if needed, but it is now visible in the Nonlinear Animation editor:

Open the Nonlinear Animation editor, you'll see the strip that contains the action:

Clicl N in order to open the panel on the right, click on the Strip tab and under Action Clip, play with the Playback Scale value in order to speed up or speed down the action:

If you want to quickly reopen the action in the Dope Sheet editor, for example if you need to edit it, select the strip and press Tab