Caption Vertical Margin
video-caption-margin-y
Sets the vertical inset for burn-in captions from the aligned edge of the frame.
video-caption-margin-y accepts an integer in pixels. Captions are offset inward from the vertical edge specified by video-caption-align. For example, with video-caption-align=bottom and video-caption-margin-y=40, captions appear 40 pixels above the bottom of the frame.
Use video-caption-margin-x to control the horizontal inset.