Here you can adjust the X/Y coordinates and the start/end time of a subtitle. Only the values in BDN.xml are changed (the PNG files are not cropped).
The toolbar contains the following buttons and controls:
Subtitles (the list on the right) - double-click a subtitle to navigate to it.
The panel at the bottom lets you adjust the Left (X) and Top (Y) coordinates as well as the start and end time of the active subtitle. You can also adjust the coordinates of a subtitle with the mouse.
The OK button closes this window and updates BDN.xml.