opencv
Utilizando VideoCapture con OpenCV Python

Leyendo cuadros desde un video pre-capturado

import numpy as np
import cv2

#access a video from your disk
#to use the GIF in this example, convert to avi!
cap = cv2.VideoCapture('eg_videoRead.avi')


#we are going to read 10 frames 
#we store the frames in a numpy structure
#then we'll generate a minimum projection of those frames

frameStack=[]
numFrames=10

for fr in range(numFrames):
    cap.set(cv2.CAP_PROP_POS_FRAMES,fr) #specifies which frame to read next
    frame=cap.read() #read the frame
    #gray = cv2.cvtColor(frame[1], cv2.COLOR_BGR2GRAY) #convert to gray scale
    frameStack.append(frame[1]) #add current frame to our frame Stack
    
minProjection=np.min(frameStack,axis=0) #find the minimum across frames
cv2.imshow("projection", minProjection) #show the result

Utilizando VideoCapture con OpenCV Java

No hay imagen en el java, necesitas escribir un método para esto. Este método es un Mat2bufferedImage. Toma el objeto mat como parámetro y devuelve la imagen.

public static void main(String[] args) {
    Mat frame = new Mat();
    //0; default video device id
    VideoCapture camera = new VideoCapture(0);
    JFrame jframe = new JFrame("Title");
    jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    JLabel vidpanel = new JLabel();
    jframe.setContentPane(vidpanel);
    jframe.setVisible(true);

    while (true) {
        if (camera.read(frame)) {

            ImageIcon image = new ImageIcon(Mat2bufferedImage(frame));
            vidpanel.setIcon(image);
            vidpanel.repaint();

        }
    }
}