Apply a boxblur algorithm to the input video.

It accepts the following parameters:

• luma_radius, lr
• luma_power, lp
• chroma_radius, cr
• chroma_power, cp
• alpha_radius, ar
• alpha_power, ap

A description of the accepted options follows.

luma_radius, lr, chroma_radius, cr, alpha_radius, ar

Set an expression for the box radius in pixels used for blurring the corresponding input plane.

The radius value must be a non-negative number, and must not be greater than the value of the expression min(w,h)/2 for the luma and alpha planes, and of min(cw,ch)/2 for the chroma planes.

Default value for luma_radius is "2". If not specified, chroma_radius and alpha_radius default to the corresponding value set for luma_radius.

The expressions can contain the following constants:

w, h

The input width and height in pixels.

cw, ch

The input chroma image width and height in pixels.

hsub, vsub

The horizontal and vertical chroma subsample values. For example, for the pixel format "yuv422p", hsub is 2 and vsub is 1.

luma_power, lp, chroma_power, cp, alpha_power, ap

Specify how many times the boxblur filter is applied to the corresponding plane.

Default value for luma_power is 2. If not specified, chroma_power and alpha_power default to the corresponding value set for luma_power.

A value of 0 will disable the effect.