Motion Threshold and Motion Damping: (available in Roto Brush 1 by default and when you enable classic controls in Next-Gen Roto Brush and 2). These two properties control how the search region is constrained based on motion. Change Motion Threshold to set the motion level below, which is considered no motion, where the search region will shrink to nothing. Motion Damping affects the remaining areas that are considered to be in motion. As you increase Motion Damping, the search region is tightened, with slow-moving areas tightening more than fast-moving areas. Constraining the search region in areas with slight motion can reduce edge chatter in these regions. Constraining the search region too much will cause the automatic boundary detection to fall off the edge of the object. You can copy Roto Brush Path properties and paste them into masks, shapes, and instances of the Paint effect, just like you can with other kinds of paths. If you copy an individual stroke, the Roto Brush span information is not copied; however, if you copy the entire Roto Brush effect instance, it includes the Roto Brush span (and base frame) information. You can change the brush size ( Diameter) for the Roto Brush tool in the same way that you change it for the paint tools. You can use the Diameter control in the Brushes panel or Ctrl-drag (Windows) or Command-drag (macOS) in the Layer panel. Other controls in the Brushes panel do affect the Roto Brush tool, with the exception of Hardness. Each time that you make a stroke within a span, the span grows unless it can't because the span in which you're drawing is next to another span: The Roto Brush Tool is similar in many ways to the paint tools, though it also has several important differences.

You can use expressions on the Roto Brush effect's Path property in the same manner as the Paint effect's Path property.