Just a quick direction to program -> fdupes
(on gentoo emerge fdupes -av)
fdupes -r movies_dir1 movies_dir2 > duplicates.txt
Above commands creates hashes of all files within specifies directories (-r recursive) and outputs that list to duplicates.txt. Now you can investigate that list and delete duplicates manualy.
You can also tell fdupes to delete files automatically or to be prompted.