How do you make this effect?

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Mask: Apply

The video filters beginning with “Mask:” let you select a portion of the image or video in which to apply other video filters. There are a few different ones, and this one goes after a sequence of other filters. There are no parameters or UI for this filter. Also, it can only be used once per clip or track. To really make this work you first add a Mask: Simple Shape, Mask: From File, or Mask: Chroma Key video filter to select the portion of the image you want to affect. Then, add one or more f…