def _find_start_end_time(stream):
    """
    find the start and end time of a specific stream.

    :param stream:
    :return starttime, endtime:
    """
    starttime = []
    endtime = []
    for tr in stream:
        starttime.append(tr.stats.starttime)
        endtime.append(tr.stats.endtime)
    return max(starttime), min(endtime)
