code: def transform_folder(args):
    
    command, (transform, src, dest) = args
    try:
      print(progress.value, "remaining")
  
      # Apply transformations to all files
      data = []
      data_dir = os.path.join(src, command)
      for filename in os.listdir(data_dir):
        path = os.path.join(data_dir, filename)
        data.append(transform({'path': path}))
  
      # Save results
      pickleFile = os.path.join(dest, "{}.pkl".format(command))
      gc.disable()
      with open(pickleFile, "wb") as f:
        pickle.dump(data, f, pickle.HIGHEST_PROTOCOL)
      gc.enable()
  
      # Update progress
      with progress.get_lock():
        progress.value -= 1
  
    except Exception as e:
      print(command, e, file=sys.stderr)
      traceback.print_exc()
docs: Transform all the files in the source dataset for the given command and save
    the results as a single pickle file in the destination dataset
    :param args: tuple with the following arguments:
                 - the command name: 'zero', 'one', 'two', ...
                 - transforms to apply to wav file
                 - full path of the source dataset
                 - full path of the destination dataset