White space above and below to add captions

The easiest way to do what you want is to create graphics containing the text you want against a white background. Have three layers (or tracks). On the bottom track put the video. On the next track up, overlay the text-graphic for the bottom text, and finally one the third track put the text-graphic for the top layer. Alternatively you use the following step:

1. From 'Project Assets' choose -> Panel Options -> New Items-> Color Matte (Select white)

2. Use a black font and Title tool on top of the matte. Resize the matte so that it's where you want the text and not cover up the video.

It's easiest, though just to make some jpegs with the text you want and add them where your want them, re-sized for the background.

It's not clear what you want to do, brad.

Are you trying to create a video that appears in a window at the top of the screen and a subtitle that runs in the lower half?