River Past Video Perspective will automatically retrieve the aspect ratio of the input video. Let's change the "Output Aspect Ratio" to "4 x 3" and change the "Scaling" to "Letterbox".
Please notice that black strips are added to the video. This is normal when "Scaling" is set to "Letterbox".
Now, let's change the "Scaling" to "Pan & Scan".
Instead of black strips, you can see the top and bottom of the origianl video are sliced off.
