Filter mandelbrot
  Render a Mandelbrot fractal.
    Inputs:
        none (source filter)
    Outputs:
       #0: default (video)
mandelbrot AVOptions:
  size              <image_size> ..FV..... set frame size (default "640x480")
  s                 <image_size> ..FV..... set frame size (default "640x480")
  rate              <video_rate> ..FV..... set frame rate (default "25")
  r                 <video_rate> ..FV..... set frame rate (default "25")
  maxiter           <int>        ..FV..... set max iterations number (from 1 to INT_MAX) (default 7189)
  start_x           <double>     ..FV..... set the initial x position (from -100 to 100) (default -0.743644)
  start_y           <double>     ..FV..... set the initial y position (from -100 to 100) (default -0.131826)
  start_scale       <double>     ..FV..... set the initial scale value (from 0 to FLT_MAX) (default 3)
  end_scale         <double>     ..FV..... set the terminal scale value (from 0 to FLT_MAX) (default 0.3)
  end_pts           <double>     ..FV..... set the terminal pts value (from 0 to I64_MAX) (default 400)
  bailout           <double>     ..FV..... set the bailout value (from 0 to FLT_MAX) (default 10)
  morphxf           <double>     ..FV..... set morph x frequency (from -FLT_MAX to FLT_MAX) (default 0.01)
  morphyf           <double>     ..FV..... set morph y frequency (from -FLT_MAX to FLT_MAX) (default 0.0123)
  morphamp          <double>     ..FV..... set morph amplitude (from -FLT_MAX to FLT_MAX) (default 0)
  outer             <int>        ..FV..... set outer coloring mode (from 0 to INT_MAX) (default normalized_iteration_count)
     iteration_count              ..FV..... set iteration count mode
     normalized_iteration_count              ..FV..... set normalized iteration count mode
     white                        ..FV..... set white mode
     outz                         ..FV..... set outz mode
  inner             <int>        ..FV..... set inner coloring mode (from 0 to INT_MAX) (default mincol)
     black                        ..FV..... set black mode
     period                       ..FV..... set period mode
     convergence                  ..FV..... show time until convergence
     mincol                       ..FV..... color based on point closest to the origin of the iterations


