For display and 'Save Stereo' the movie may be surrounded by a frame of a chosen color and thickness
Normally, we try to avoid the edges of the movie being positioned in front of the 'stereo window'.
This is often called a 'window violation'.
It has been suggested by some that in certain circumstances, window violation has it's uses and a fuzzy border can reduce the 'retinal rivalry' this causes.
The 'Fuzzy Border' option allows you to enable a fuzzy border and define it's size.
(Cactus image courtesy of Ai)
The displayed image-area will, of course, be reduced.
The Preferences dialog-box may be displayed with <Shift+B>.
A color may be chosen from one of 48 predefined colors or 16 custom-defined colors.
When side-by-side movies are displayed, you may choose the spacing as 'Narrow', 'Medium' or 'Wide'and toggle between them with the 'E' key.
The option here allows you to set your preferred default, spacing-mode.