Combining portrait (vertical) and landscape (horizontal) clips in one file

[Jorge15]

I am using both types of clips (portrait-vertical and landscape-horizontal) to build a single video file, to be displayed in a horizontal (PC) screen.

By default the program is building it vertically and reducing the size of the horizontal clips to match a (narrow) vertical screen. 

How can I change it to all the way around: I want the horizontal clips to show at max size (using the whole horizontal display) and show the vertical clips in the middle of the horizontal screen (with black spaces at both sides).

I am using VideoPad Professional v 10.18

thanks

Jorge