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Filed under: Motion Graphics •

Managing Moving Masks

This sequence of figures shows the difference between using the normal mask interpolation system in After Effects (the red shape) and Smart Mask Interpolation (the green shape). The secret to making this work is to align the First Vertex Point to the top or bottom center of the shapes.

Mask Speed

One “gotcha” that’s not immediately obvious with Smart Mask Interpolation is the issue of animation speed: SMI ignores any work you’ve done with the velocity curves controlling the speed of your Mask Shape’s interpolation, replacing them with a linear progression. This is a bummer if, say, you’ve decided it would be best to ease between shapes.

It’s possible to remedy this using Time Remapping. After you’ve applied SMI, select the layer and Pre-compose it, choosing the “Move All Attributes” option. Then apply Layer > Time Remapping to the resulting nested precomp (not to the original layer, which now resides inside the precomp). Edit the Time Remap keyframes as needed to get your desired pace of animation.

Great - but now you have a new problem that shows up if you try to ease into or out of your shapes: The Mask Shape goes absolutely wacky between the first original keyframe and the first SMI keyframe, and equally wacky between the last SMI keyframe and the last original keyframe. This is because After Effects gets completely confused as it tries to interpolate between the original shape, which had relatively few vertices, and the first SMI shape which has a ton of vertices.

There are a couple of workarounds for this. Your first instinct might be to increase SMI’s Keyframe Rate to as high as possible. This would reduce the time gap between the original and SMI keyframes, reducing the chance you will see this odd interpolation. However, After Effects does not allow you to set a frame rate higher than 99 fps; in practice, you may need a frame rate roughly 15 times normal to hide any glitch that would appear with a simple ease in/out. The better approach is to set up your original Mask Shape animation to take far longer than you will eventually need - say, 20:00 seconds between keyframes instead of the desired 01:00. Then when you Time Remap, speed up the overall animation to finish when you need it to. This will also reduce the time gap between “real” and SMI keyframes, hopefully burying the glitch (as always, RAM Preview before committing to a final render!).

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