Filter cover_rect
  Find and cover a user specified object.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
cover_rect AVOptions:
  cover             <string>     ..FV.... cover bitmap filename
  mode              <int>        ..FV.... set removal mode (from 0 to 1) (default blur)
     cover                        ..FV.... cover area with bitmap
     blur                         ..FV.... blur area


