def extract_info(j):
    """
    return info dict

    info = {
        id := str,
        title := str,
        index := int,
        filename := str
        playlist_title := str
    }
    """
    return dict((
        ("id", j["display_id"]),
        ("title", j["title"]),
        ("index", j["playlist_index"]),
        ("filename", j["_filename"]),
        ("playlist_title", j["playlist_title"]),
    ))