Final Cut Pro 10.4’s masks and mask effects are not 360° spherical video aware. When the edge of masks are blurred to make them softer – ‘feathered’ – the blur is not 360° aware. To make an edge blur consistent when looking around the sphere, the source equirectangular edge must be blurred much more nearer the top and bottom of the clip.
360° Longitude Mask 4D is in the Masks category of Alex4D 360° Effects:
Here is what the Final Cut Pro 360° viewer and the viewer look like when the 360° Longitude Mask 4D effect is applied:
Mask Opacity sets how opaque the chosen longitudes are.
Longitude and Mask Width set the longitude of the mask and its width. They can be set using the on-screen control. A Longitudeof 0.5 corresponds to 0°, 0 to 180° West, 1 to 180° East.
Mask Feather controls the softness of the edge of the mask.
Invert Mask shows everything outside the selected longitudes, and hides everything inside.
Original Opacity sets how opaque the area outside the chosen longitudes are.