Did you set Video.as as your document class in Animate? I suspect that this error could happen if you accidentally set source/feathers/examples/video/Main.as as the document class instead.
If Video.as is your document class, then the only other thing that I can think of is that you modified Main.as to import
flash.display.Sprite instead of
starling.display.Sprite. It seems unlikely that you'd do that, though, so I lean toward the wrong document class as the likely culprit.