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BoxBlur

Based on ffmpeg’s boxblur, this is a very fast algorithm which can be used to blur horizontal, vertical, and at a power level. Simplest usage is to just blur the entire image but with the following parameters, you can create a specific rectangular section to blur instead.

X/Y:
  point coordinates of a rectangular box to be blurred. X and Y of 0 are in the upper left hand corner. Default to be blurred is the entire image.
Drag:
  is used when you want to create just a rectangular area to be blurred rather than the enire image. If you used keyframes to cover a moving area and had left the Drag box enabled, you can remove the drag box with Allow keyframe spanning whose use is described in Allow Keyframe Spanning.
W/H
  the values in these 2 boxes specify the width and height of the drag area box measured in pixels as shown in the compositor window. You can set these manually and if you can not see the location of your box, set them to zero because 0 sets it to the same as the width/height of the project.
Horiz:
  slider goes from 0 to 100. Increasing this horizontal number, increases the blurriness in the horizontal direction. The default value is 2. You can also use the mouse wheel to scroll the slider. There is a clear button on the right to set the value to 0.
Vert:
  slider goes from 0 to 100. Increasing this vertical number, increases the blurriness in the vertical direction. The default value is 2. You can also use the mouse wheel to scroll the slider. There is a clear button on the right to set the value to 0.
Power:
  the way Power works is like stacking up the blur multiple times. For example, a power of 3 would be like blurring once, then blurring that again, and finally blurring that a third time. The slider varies from 1 to 10 with 2 being the default value. There is a clear button on the right to set the value to 1.
Reset:
  button to revert to the default values and turn off Drag if it is on.