@classmethod
def silent(cls, duration=1000, frame_rate=11025):
    """
        Generate a silent audio segment.
        duration specified in milliseconds (default duration: 1000ms, default frame_rate: 11025).
        """
    frames = int(frame_rate * (duration / 1000.0))
    data = b'\x00\x00' * frames
    return cls(data, metadata={'channels': 1, 'sample_width': 2,
        'frame_rate': frame_rate, 'frame_width': 2})
