docs: private HashSet<Resource> preferMp3(HashSet<Resource> files) {
      HashMap<String, Resource> map = new HashMap<String, Resource>();
      for (Resource file : files) {
        String path = stripExtension(file.getPath());
        if (file.getPath().endsWith(".mp3") || !map.containsKey(path)) {
          map.put(path, file);
        }
      }
      return new HashSet<Resource>(map.values());
    }