def generate_file_name(file_name="playlist", resolution="SD", extention="m3u8"):
    """ return file name with resulotion
    ex: generate_file_name('output', 'HD')
        >> 'output_HD.m3u8
    """
    if file_name is None: file_name="playlist"
    if extention is None: extention="m3u8"
    
    return f"{file_name}_{resolution}.m3u8"