Filter find_rect
  Find a user specified object.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
find_rect AVOptions:
  object            <string>     ..FV..... object bitmap filename
  threshold         <float>      ..FV..... set threshold (from 0 to 1) (default 0.5)
  mipmaps           <int>        ..FV..... set mipmaps (from 1 to 5) (default 3)
  xmin              <int>        ..FV.....  (from 0 to INT_MAX) (default 0)
  ymin              <int>        ..FV.....  (from 0 to INT_MAX) (default 0)
  xmax              <int>        ..FV.....  (from 0 to INT_MAX) (default 0)
  ymax              <int>        ..FV.....  (from 0 to INT_MAX) (default 0)


