How to write sequence of frames to video file in cv2

cv2.videoWrite.py

def write_avi(frames, path):
    '''
    frames - 3D numpy array (seq, height, width)
    path - result avi file path. Extantion of file have to be .avi
    '''
    def norm(x):
        x = x - x.min()
        x = x / x.max()
        return (x*255).astype(np.uint8)
    frames = norm(frames)
    fourcc_string = 'MJPG'
    fourcc = cv2.VideoWriter_fourcc(*fourcc_string)
    out = cv2.VideoWriter(path, fourcc, fps, frames.shape[1:][::-1])
    for i in range(len(frames)):
        out.write(np.repeat(frames[i][...,np.newaxis],3,-1))
    out.release()