Add paddings to the input image, and place the original input at the provided x, y coordinates.

It accepts the following options:

width, w, height, h

Specify an expression for the size of the output image with the paddings added. If the value for width or height is 0, the corresponding input size is used for the output.

The width expression can reference the value set by the height expression, and vice versa.

The default value of width and height is 0.

x, y

Specify the offsets to place the input image at within the padded area, with respect to the top/left border of the output image.

The x expression can reference the value set by the y expression, and vice versa.

The default value of x and y is 0.

If x or y evaluate to a negative number, they’ll be changed so the input image is centered on the padded area.

color

Specify the color of the padded area. For the syntax of this option, check the "Color" section in the ffmpeg-utils manual.

aspect

Pad to an aspect instead to a resolution.

The value for the width, height, x, and y options are expressions containing the following constants:

in_w, in_h

The input video width and height.

iw, ih

These are the same as in_w and in_h.

out_w, out_h

The output width and height (the size of the padded area), as specified by the width and height expressions.

ow, oh

These are the same as out_w and out_h.

x, y

The x and y offsets as specified by the x and y expressions, or NAN if not yet specified.

a

same as iw / ih

sar

input sample aspect ratio

dar

input display aspect ratio, it is the same as (iw / ih) * sar