Correct perspective of video not recorded perpendicular to the screen.

A description of the accepted parameters follows.

x0, y0, x1, y1, x2, y2, x3, y3

Set coordinates expression for top left, top right, bottom left and bottom right corners. Default values are 0:0:W:0:0:H:W:H with which perspective will remain unchanged. If the sense option is set to source, then the specified points will be sent to the corners of the destination. If the sense option is set to destination, then the corners of the source will be sent to the specified coordinates.

The expressions can use the following variables:

W, H

the width and height of video frame.

in

Input frame count.

on

Output frame count.

interpolation

Set interpolation for perspective correction.

It accepts the following values:

• linear
• cubic

Default value is linear.

sense

Set interpretation of coordinate options.

It accepts the following values:

0, source

Send point in the source specified by the given coordinates to the corners of the destination.

1, destination

Send the corners of the source to the point in the destination specified by the given coordinates.

Default value is source.

eval

Set when the expressions for coordinates x0,y0,...x3,y3 are evaluated.

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.