Alex4D Trim works in the same way as the trim mode of the crop effect, with an extra. You can blur all the edges using the ‘Overall Feather’ parammeter, and have additional individual feather values for each edge of the trim.
I’ve also included versions of this effect that trim a single edge.
Download the effect archive from here.
Expand the ZIP archive and add the folders to Movies : Motion Templates : Effects : Alex4D :
If you don’t have Motion installed on your Mac and you’ve never installed any third-party effects, download the archive of the Motion Templates folder with the Trim effects in the correct sub-folder. Expand the ZIP and put the resulting Motion Templates folder in the Movies folder of your home folder.
If you find this free plugin useful, you might like my Alex4D Animation Transitions plugin pack:
There are many more free plugins on my Final Cut Pro X page