def __init__(self, audio, win_len=0.01):
    """Create an AudioVolume instance.

    :param audio: (AudioPCM) The audio to work on.
    :param win_len: (float) Window length to estimate the volume.

    """
    super(AudioVolume, self).__init__(win_len)
    pos = audio.tell()
    audio.rewind()
    nb_frames = int(win_len * audio.get_framerate())
    nb_vols = int(audio.get_duration() / win_len) + 1
    self._volumes = [0.0] * nb_vols
    i = 0
    while audio.tell() < audio.get_nframes():
        frames = audio.read_frames(nb_frames)
        a = AudioFrames(frames, audio.get_sampwidth(), audio.get_nchannels())
        self._volumes[i] = a.rms()
        i += 1
    audio.seek(pos)
    self._rms = audio.rms()