When I release an iMovie project to iTunes to be viewed via Apple TV, it creates in the background a sharing file which consumes a lot of space on the storage disc.
What is the function of this sharing file?
So you can re-edit it directly in iMovie and it will be updated in iTunes (since it is the same shared file).
Just export it from iMovie and add it to iTunes.
It'll create a new .m4a file but it won't be shared.