def get_maximum_time(note_tracks):
    """
    Determines the largest value of end_time
    among all notes. This is required to know
    when the video should end.
    """
    maximum_time = -999999.9
    for t in note_tracks:
        for pitch_list in t:
            if pitch_list != []:
                if pitch_list[-1].end_time > maximum_time:
                    maximum_time = pitch_list[-1].end_time
    return maximum_time