How do you animate a mask position in After Effects?

You can animate a mask position in After Effects by creating keyframes for the mask path.

Animating Mask Position: A Step-by-Step Guide

To animate the position of a mask in Adobe After Effects, follow these steps:

Select the Layer: First, select the layer with the mask you want to animate. This is usually done in the timeline panel.
Open Mask Properties: Expand the layer's properties by clicking the arrow to the left of the layer's name. Then, expand the "Masks" property to reveal the masks associated with that layer.
Locate the Mask Path: Find the specific mask you want to animate and expand its properties. You should see a property called "Mask Path".
Enable Keyframing: To enable animation, click the stopwatch icon to the left of the "Mask Path" property. This will create a keyframe at the current time indicator position and turn the stopwatch blue. The keyframe indicates the starting point of your animation. As indicated by the provided reference, you must create keyframes for the mask path to animate it.
Move the Time Indicator: Move the current time indicator in the timeline to a new point in time where you want the mask to be in a different position.
Adjust the Mask: Select the mask using the selection tool in the Composition panel. Now you can adjust the mask's position and shape using the handles that appear.
Create New Keyframes: When you adjust the mask, a new keyframe will be automatically created at the new time indicator position, capturing the changed position.
Preview Your Animation: Play back your composition to preview the mask's animation, which will transition smoothly from keyframe to keyframe.

Keyframes are essential for animation.

A keyframe marks a point in time where a property, like the mask path, has a specific value.
After Effects interpolates, or fills in the gaps, between these keyframes, creating the animation.
You can add more keyframes to create complex animations.

Ease In/Out: Use ease in/out keyframe interpolation to make transitions feel smoother and more natural. Right-click the keyframes in the timeline and go to Keyframe Assistant > Easy Ease, or Easy Ease In, or Easy Ease Out.
Fine-tune: Adjust the keyframe positions and mask shape to refine your animation, including adjusting the mask path itself, to achieve the exact motion you desire.
Graph Editor: Use the Graph Editor for more control over the speed and motion of your animation by manipulating the curves between keyframes.