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Masks define which parts of a clip are visible. Masterselects renders masks on the GPU: shapes are rasterized on the CPU with Canvas2D, then passed to the composite shader as a texture where feathering and inversion are applied in a single WGSL pass. You can add multiple masks to a single clip and combine them with mask modes to build complex cutouts.

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Mask types

Rectangle

Click and drag to define the corners. Instant creation, ideal for hard-edged crops.

Ellipse

Click and drag to define the bounding box. Uses a cubic Bézier approximation for a smooth circle.

Pen tool

Click to add vertices and build a freeform path. Double-click on the first vertex or the last to close the path.

Bézier path

Click and drag when placing a vertex to pull out Bézier handles and create smooth curves.

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Creating your first mask with the pen tool

1

Select the clip

Click the clip you want to mask on the timeline.
2

Choose the pen tool

In the Properties panel, open the Masks section and click the pen tool icon.
3

Place vertices

Click in the preview canvas to place each vertex. Drag while clicking to create curved Bézier segments.
4

Close the path

Click the first vertex again, or double-click the last vertex, to close the shape.
5

Adjust feathering

Use the Feather slider to soften the mask edge. Values are in pixels (0–50).

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Feathering

The feather slider controls a GPU blur applied to the mask edge. The quality tier is selected automatically based on the feather radius:
QualityKernel tapsFeather range
Low17-tap1–33 px
Medium33-tap34–66 px
High61-tap67–100 px
Adjust Feather Quality (1–100) independently of the feather radius if you need finer or coarser blurring at the same edge size.

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Mask modes

Every mask has a mode that controls how it combines with the masks below it:
ModeBehavior
AddReveals the area inside the mask. Multiple Add masks union together.
SubtractHides the area inside the mask. Cuts holes in the masks below it.
IntersectShows only the area where this mask overlaps with the masks below it.
Example — rectangle with a circular hole:
  1. Add a rectangle mask (mode: Add)
  2. Add an ellipse mask over the center (mode: Subtract)

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Invert

Enable the Invert toggle on any mask to flip which area it reveals. An inverted Add mask hides the interior and shows the exterior.

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Editing vertices

  • Click a vertex to select it (turns cyan).
  • Drag a selected vertex to reposition it.
  • Drag a segment between two vertices to move both simultaneously — useful for reshaping edges without selecting individual points.
  • Shift + drag a Bézier handle to scale both handles proportionally.
  • Press Delete or Backspace to remove a selected vertex.

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Animating mask shapes

Mask vertices are keyframeable. With the clip selected, enable keyframing on a vertex position and move the playhead to a new time before repositioning the vertex. The shape interpolates between keyframe states during playback.
Mask tracking and rotobézier auto-smooth are not yet implemented. Animated mask paths require manually placing keyframes on each vertex.

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Multiple masks per clip

You can stack any number of masks on a single clip. Masks evaluate top-to-bottom — drag the mask rows to reorder them. Each mask has independent feather, opacity, mode, and invert settings.

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