Configure FFmpeg swaprect Filter Coordinates

This guide explains how to configure the dimensions and coordinates of the two rectangular regions used in the FFmpeg swaprect video filter. You will learn the exact syntax, the parameter definitions, and how to apply practical examples to swap specific areas within a video frame.

The swaprect Syntax

The swaprect filter swaps two rectangular areas of the same size within a video. The basic syntax for the filter is:

swaprect=w:h:x1:y1:x2:y2

Each parameter defines the size or position of the rectangles:

• w: The width of both rectangular areas.
• h: The height of both rectangular areas.
• x1: The horizontal (X) coordinate of the top-left corner of the first rectangle.
• y1: The vertical (Y) coordinate of the top-left corner of the first rectangle.
• x2: The horizontal (X) coordinate of the top-left corner of the second rectangle.
• y2: The vertical (Y) coordinate of the top-left corner of the second rectangle.

Available Constants

Instead of using strictly static pixel values, you can use built-in FFmpeg constants to make your coordinates dynamic:

• w or iw: Input video width.
• h or ih: Input video height.
• a: Aspect ratio (input width divided by input height).
• sar: Sample aspect ratio.
• dar: Display aspect ratio.

Practical Examples

Example 1: Swapping Top-Left and Top-Right Corners

To swap a 200x150 pixel area from the top-left corner (0,0) with a 200x150 pixel area in the top-right corner of a video, use the following command:

ffmpeg -i input.mp4 -vf "swaprect=200:150:0:0:iw-200:0" -c:a copy output.mp4

In this command: * w is 200 and h is 150. * The first rectangle is positioned at x1=0, y1=0. * The second rectangle is positioned at x2=iw-200 (input width minus the rectangle width) and y2=0.

Example 2: Swapping Left and Right Halves of a Video

To swap the left half of a video with the right half, set the width of the rectangles to half of the input width (iw/2) and the height to the full input height (ih):

ffmpeg -i input.mp4 -vf "swaprect=iw/2:ih:0:0:iw/2:0" -c:a copy output.mp4

In this command: * w is iw/2 (half the width) and h is ih (full height). * The first rectangle starts at 0:0. * The second rectangle starts at iw/2:0.