AE : Using a drawn brush as a mask

Question

Is there a way to mask brush strokes like you can with a pen?

At present, Im using a pen to create a mask then generate a stroke (Effects>Generate>Stroke).

I then use reveal putting a keyframe on the end of the effect to reveal the comp following the pen's stroke if that makes sense.

I want to use the same type of effect by revealing a larger background image, but the stroke's maximum width using the above technique is 50 which is not big enough.

From what i understand, brush strokes are vectors in AE so is the same type of thing possible using a brush to create a mask?

thanks

Answer 1

If you use the brush on a layer, it actually applies the "paint" effect to the layer. If you paint on a layer with the brush and expand the properties for effects>paint>brush 1> you'll see that there is a start and end setting that can be animated, allowing you to animate the stroke.

Answer 2

Paint on a solid layer (in the layer panel). Select the path of the paint object by putting a keyframe on the paint effect's brush in the timeline and copying that keyframe.

Now add a mask by right-clicking on the layer and choosing a 'new mask'. Put a keyframe in the mask on the timeline. Select that keyframe and paste.

Now you can turn off the eyeball on the paint effect and you'll have it's shape as a unstroked mask on that mask keyframe. Select that mask path keyframe (you may or may not see the control points) and apply a stroke.

Thicken up the stroke (with 'Brush Size' in the Stroke effect in the timeline) until you like it. Make the stroke white. Now add a Key effect - probably you'll want a 'Luma Key.' Switch the view from the Layer view to the Composition view. In the timeline, under the Luma Key effect, select 'Key Out Brighter' and the dial in the correct 'Threshold' until you can see the layer below (you've got one, right?)

That's how to turn a brush stroke into a mask.