import cv2
import matplotlib.pyplot as plt

class Viewer:
    def __init__(self, video_filename):
        self.cap = cv2.VideoCapture(video_filename)
        self.ax1 = plt.subplot(1, 2, 1)
        self.ax2 = plt.subplot(1, 2, 2)

        # Grab the first frame.
        frame = self.grabframe()
        self.im1 = self.ax1.imshow(frame)
        self.im2 = self.ax2.imshow(frame)

    def grabframe(self):
        ret, frame = self.cap.read()
        if ret:
            return frame
        else:
            print('[ERROR] grabframe failed')
            return self.grabframe()

    def update(self, frame):
        """Update the display."""
        print('[INFO] updating...')
        self.im1.set_data(frame)
        self.im2.set_data(frame)
        plt.draw()


def main():
    """Run it."""
    cli = argparse.ArgumentParser()
    cli.add_argument('-i', '--input', type=str, required=True)
    args = cli.parse_args()

    viewer = Viewer(args.input)

    while True:
        viewer.update(viewer.grabframe())

if __name__ == '__main__':
    plt.ion()
    plt.show()
    main()