Shutter angle is one of the ways to set the time of exposure for video. With the fp, it is the STILL mode shutter speed.
This represents the time of exposure as a percentage of the time per frame, which is determined by the frame rate (e.g. 1/30 second at 30 fps) expressed as an angle where 360° is 100%.
For instance, 180° at 30 fps is 1/60 of a second; 180° at 120 fps is 1/240 of a second.