pad - FFmpeg 7.1 / Filters / Video

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

It accepts the following parameters:

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.

The default value of color is "black".

eval

Specify when to evaluate width, height, x and y expression.

It accepts the following values:

init: Only evaluate expressions once during the filter initialization or when a command is processed.
frame: Evaluate expressions for each incoming frame.

Default value is init.

aspect

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

Examples

Add paddings with the color "violet" to the input video. The output video size is 640x480, and the top-left corner of the input video is placed at column 0, row 40
```
pad=640:480:0:40:violet
```
The example above is equivalent to the following command:
```
pad=width=640:height=480:x=0:y=40:color=violet
```
Pad the input to get an output with dimensions increased by 3/2, and put the input video at the center of the padded area:
```
pad="3/2*iw:3/2*ih:(ow-iw)/2:(oh-ih)/2"
```
Pad the input to get a squared output with size equal to the maximum value between the input width and height, and put the input video at the center of the padded area:
```
pad="max(iw\,ih):ow:(ow-iw)/2:(oh-ih)/2"
```
Pad the input to get a final w/h ratio of 16:9:
```
pad="ih*16/9:ih:(ow-iw)/2:(oh-ih)/2"
```
In case of anamorphic video, in order to set the output display aspect correctly, it is necessary to use sar in the expression, according to the relation:
```
(ih * X / ih) * sar = output_dar
X = output_dar / sar
```
Thus the previous example needs to be modified to:
```
pad="ih*16/9/sar:ih:(ow-iw)/2:(oh-ih)/2"
```
Double the output size and put the input video in the bottom-right corner of the output padded area:
```
pad="2*iw:2*ih:ow-iw:oh-ih"
```