Filter gradients
  Draw a gradients.
    slice threading supported
    Inputs:
        none (source filter)
    Outputs:
       #0: default (video)
gradients 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")
  c0                <color>      ..FV...... set 1st color (default "random")
  c1                <color>      ..FV...... set 2nd color (default "random")
  c2                <color>      ..FV...... set 3rd color (default "random")
  c3                <color>      ..FV...... set 4th color (default "random")
  c4                <color>      ..FV...... set 5th color (default "random")
  c5                <color>      ..FV...... set 6th color (default "random")
  c6                <color>      ..FV...... set 7th color (default "random")
  c7                <color>      ..FV...... set 8th color (default "random")
  x0                <int>        ..FV...... set gradient line source x0 (from -1 to INT_MAX) (default -1)
  y0                <int>        ..FV...... set gradient line source y0 (from -1 to INT_MAX) (default -1)
  x1                <int>        ..FV...... set gradient line destination x1 (from -1 to INT_MAX) (default -1)
  y1                <int>        ..FV...... set gradient line destination y1 (from -1 to INT_MAX) (default -1)
  nb_colors         <int>        ..FV...... set the number of colors (from 2 to 8) (default 2)
  n                 <int>        ..FV...... set the number of colors (from 2 to 8) (default 2)
  seed              <int64>      ..FV...... set the seed (from -1 to UINT32_MAX) (default -1)
  duration          <duration>   ..FV...... set video duration (default -0.000001)
  d                 <duration>   ..FV...... set video duration (default -0.000001)
  speed             <float>      ..FV...... set gradients rotation speed (from 1e-05 to 1) (default 0.01)


