11. Motion  Motion Threshold and Dampening define how the search area responds to motion. The default of 50 per cent is good but a well-defined figure running across a scene may need an increased Threshold and lower Dampening. For a relatively still figure you could increase Dampening to sharpen the edges of the mask.

12. The matte  Check Refine Matte to further edit the matte, best seen in Alpha view. Smooth, Feather and Choke work as in other keying controls, while Reduce Chatter determines how tightly the edge stays with the selection. If the selection isn’t moving much but the edges change erratically increase this value, and vice versa.

13. Cleaning  Decontamination removes background colour from the edge of the selection. This area can be checked to be seen. All values can be keyframed and adjusted across the span. Initialise keyframing by clicking the stopwatch next to the property. Moving the playback head and altering a value creates a keyframe.

14. Freezing  If you have made a good selection constant across frames you can expand the span by dragging on the end frames. In particularly difficult situations you can add more spans by painting on the clip outside the current span. When finished press Freeze to preserve the selection information for another edit session.