AphelionRotoscoping and animated masks in Aphelion Editor
Rotoscoping is what you do when a key cannot do the job: a soft edge, a shadow, an object with no colour separation from its background. Aphelion builds these as Bezier shapes that animate over time, and hands them to a tracker when the movement is better described than drawn.
Shapes, drawn and animated
A roto shape is a closed Bezier outline rasterised into a matte. Points are placed in the viewport, and any point can be keyframed, so a shape can change both its position and its outline over the length of a shot — which is what a matte following a turning head actually needs.
The rasterised matte is a full frame-sized greyscale image, so it plugs into the same mask sockets as a keyer's output. There is no separate “roto mode”: a hand-drawn matte and an extracted one are the same kind of value and combine freely.
Feather and choke are applied to the rasterised matte rather than to the shape, so a soft edge behaves like a soft edge rather than like an inflated polygon.
Shape tracking
A plain point tracker follows a pixel pattern, which fails on soft or low-contrast features. Shape tracking inverts the problem: you describe the region you care about as an outline, and the tracker follows that region, translating the whole matte with it.
That makes it the right tool for following the movement of something without a crisp feature — a shadow, a gradient, a soft-edged object — where you know the shape and only need to know where it went.
Because the shape's motion comes out as ordinary properties, it can be combined with a hand-animated offset, driven by a keyframe curve, or split so that tracking and manual correction each own part of the movement.
Shape Tracker reference · Tutorial: Shape Tracker masks · Tutorial: roto and masks