Filter drawbox
  Draw a colored box on the input video.
    Inputs:
       #0: default (video)
    Outputs:
       #0: default (video)
drawbox AVOptions:
  x                 <string>     ..FV.... set horizontal position of the left box edge (default "0")
  y                 <string>     ..FV.... set vertical position of the top box edge (default "0")
  width             <string>     ..FV.... set width of the box (default "0")
  w                 <string>     ..FV.... set width of the box (default "0")
  height            <string>     ..FV.... set height of the box (default "0")
  h                 <string>     ..FV.... set height of the box (default "0")
  color             <string>     ..FV.... set color of the box (default "black")
  c                 <string>     ..FV.... set color of the box (default "black")
  thickness         <string>     ..FV.... set the box thickness (default "3")
  t                 <string>     ..FV.... set the box thickness (default "3")

This filter has support for timeline through the 'enable' option.

