When you import movies into iMovie 10 libraries, the file is always copied, wasting space and hindering editability. This script replaces the copy with a hardlink, reclaiming disk space.

dedup-imovie-library

#!/usr/bin/env ruby

# Usage: dedup-imovie-library LIBRARY ORIGINALS
#
# Goes through an iMovie 10 library and replaces all the "Original Media" with
# symlinks to the actual original media, in order to conserve disk space. Note
# that because they're symlinks, if the path to the originals changes (e.g. you 
# rename the external drive they are on) then the links will be broken.
#
# This assumes you've already imported the files into iMovie and waited for them
# all to be copied.
#
# This also assumes movie files in LIBRARY have unique matches in ORIGINALS with
# the same filename!
#
# This script will also check that the file is indeed a duplicate before deleting it and creating a link

require 'fileutils'

library = ARGV.shift
originals = ARGV.shift

fail "Library #{library} does not exist" unless library && File.exist?(library)
fail "You must use an absolute path for the originals directory" if originals.start_with?( '..')
fail "Originals folder #{originals} does not exist" unless originals && File.exist?(originals)

# For each original file in the imovie library
Dir.glob(File.join(library, '**', 'Original Media', '*')) do |library_file|
  next unless File.file? library_file

  # Skip it if we've already replaced it with a hardlink
  #next if File.stat(library_file).nlink > 1
  
  # Skip it if we've already replaced it with a symlink
  next if File.lstat(library_file).symlink?

  original = Dir.glob(File.join(originals, '**', File.basename(library_file))).first

  next unless original

  # Make sure file contents are identical
  next unless FileUtils.compare_file library_file, original
  
  puts "Linking #{library_file} => #{original}"
  FileUtils.rm_f library_file, verbose: true
  
  # Replace with a hardlink
  #FileUtils.ln original, library_file, verbose: true
  
  # Replace with a symlink
  FileUtils.ln_s original, library_file, verbose: true
end

Forked and updated to check that the file is a true duplicate before replacing it.
Also switched to using symlinks instead