import ast


def get_clip_action_label(row):
    """
    Get the action label of the positive clips.
    This function requires the output from VIA tool contains a column 'metadata'.

    :param row: pandas.Series.
        One row of the video annotation output.
    :return: str.
    """
    label_dict = ast.literal_eval(row.metadata)
    track_key = list(label_dict.keys())[0]
    return label_dict[track_key]