Traverses directory collecting input and target files.

  Args:
   directory: base path to extracted audio and transcripts.
  Returns:
   list of (media_base, media_filepath, label) tuples

def _collect_data(directory):
  """Traverses directory collecting input and target files.

  Args:
   directory: base path to extracted audio and transcripts.
  Returns:
   list of (media_base, media_filepath, label) tuples
  """
  # Returns:
  data_files = []
  transcripts = [
      filename for filename in os.listdir(directory)
      if filename.endswith(".csv")
  ]
  for transcript in transcripts:
    transcript_path = os.path.join(directory, transcript)
    with open(transcript_path, "r") as transcript_file:
      transcript_reader = csv.reader(transcript_file)
      # skip header
      _ = next(transcript_reader)
      for transcript_line in transcript_reader:
        media_name, label = transcript_line[0:2]
        filename = os.path.join(directory, media_name)
        data_files.append((media_name, filename, label))
  return data_files