B-spline

You need a curve that doesn't snap through every control point but glides elegantly between them — that's a B-spline. Unlike the classic Bézier curve, which touches all anchor points, the B-spline partially ignores the control points. The result: smoother, more predictable movements without the annoying "overshoot" problem of Bézier. You'll rarely need this on set. In VFX houses and for motion tracking, it's daily bread.

The practical side: When you need to track a roto mask over 200 frames or lay a tracking point over a complex motion pattern, your compositor uses B-splines. They give you four to six control points, the curve itself runs between them — and remains mathematically stable. No jitters, no artifacts. The order of the spline determines how "loose" the curve sits: Linear (order 2) is a polyline, cubic (order 4) is buttery smooth. You'll almost always use cubic.

Practical example from rotoscoping: You're masking a moving car. With Bézier, you need 40–50 keyframes for smooth curves. With B-spline: 12–15 control points, the curve fills the gaps. Adjustments are also beneficial — moving a control point only affects its immediate vicinity, not the entire timeline like with Bézier. This saves you hours in "fine-tuning".

Important note: B-splines are not the same as NURBS (Non-Uniform Rational B-Splines), although NURBS builds upon them. You only need NURBS when dealing with 3D geometry and surface modeling — rather rare in 2D roto. In Nuke, After Effects, or Mocha, you implicitly use B-splines when the software offers "smooth curves". Some tools simply call them "Cubic Splines" — it's the same principle. The key advantage: You can still adjust B-spline keyframes later with minimal effort because the mathematical definition remains robust.