On a surprisingly regular basis I see people asking for help with making widescreen masks in FCP. I dislike using the widescreen filter in FCP for a few reasons. First, you have to apply it to each clip which is clunky and makes it very difficult if you want to go back and make changes. Second, the filter has very limited re-framing options and you can’t use the Motion tab to re-frame either because the mask gets re-framed as well. Finally, some times it’s just cumbersome to get the mask exactly how you want it.
A work around to many of the these problems is to nest the sequence and then apply the filter to the nest but then you are stuck working w/nests which can get squirrely.
My solution is pretty simple. Just use slugs. Put two slugs on high up video tracks and use the top slug to mask off the top of the frame and the bottom slug to mask off the bottom of the frame. You can easily adjust the mask to any size you want, re-framing the footage underneath is a breeze, and if decide you won’t want the mask it’s as simple as deleting the two slugs. Another great thing about using slugs is that’s a program agnostic solution.