Java open CV hangs on VideoCapture for file if openCV is loaded with nu.pattern.OpenCV.loadShared();

Question

I have a sample code from https://ratiler.wordpress.com/2014/09/08/detection-de-mouvement-avec-javacv/ with small difference in loading the open cv library in the static block using nu.pattern.OpenCV.loadShared(); :

import java.awt.image.BufferedImage;
import java.io.ByteArrayInputStream;
import java.io.IOException;
import java.io.InputStream;

import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;

import org.opencv.core.CvType;
import org.opencv.core.Mat;
import org.opencv.core.MatOfByte;
import org.opencv.core.Size;
import org.opencv.imgcodecs.Imgcodecs;
import org.opencv.videoio.VideoCapture;
import org.opencv.imgproc.Imgproc;

public class JavaCVPrjt01 {
    static {
        //System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        nu.pattern.OpenCV.loadShared();
    }
    public static void main(String[] args) {
        JFrame jframe = new JFrame("HUMAN MOTION DETECTOR FPS");
        jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JLabel vidpanel = new JLabel();
        jframe.setContentPane(vidpanel);
        jframe.setSize(1280,720) ;
        jframe.setVisible(true);

        Mat frame = new Mat();
        Mat outerBox = new Mat();
        Size sz = new Size(1280,720);
        VideoCapture camera = new VideoCapture("D:/Downloads/video4.mp4");

        while (true) {
            if (camera.read(frame)) {
                Imgproc.resize(frame,frame, sz );
                outerBox = new Mat(frame.size(), CvType.CV_8UC1);
                Imgproc.cvtColor(frame, outerBox, Imgproc.COLOR_BGR2GRAY);
                Imgproc.GaussianBlur(outerBox, outerBox, new Size(3, 3), 0);

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

            }
        }
    }

    public static BufferedImage Mat2bufferedImage(Mat image) {
        MatOfByte bytemat = new MatOfByte();
        Imgcodecs.imencode(".jpg", image, bytemat);
        byte[] bytes = bytemat.toArray();
        InputStream in = new ByteArrayInputStream(bytes);
        BufferedImage img = null;
        try {
            img = ImageIO.read(in);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return img;
    }

}

and of course, the needed dependencies were added:

    <dependency>
        <groupId>org.bytedeco.javacpp-presets</groupId>
        <artifactId>opencv</artifactId>
        <version>3.2.0-1.3</version>
    </dependency>

    <dependency>
        <groupId>org.openpnp</groupId>
        <artifactId>opencv</artifactId>
        <version>3.2.0-1</version>
    </dependency>

so, code is executed right before

VideoCapture camera = new VideoCapture("D:/Downloads/video4.mp4");

where it hangs and I have no clues to check what is wrong on the JNI level there.

Answer 1

It was a licensing issue that made impossible to include ffmpeg to

 <dependency>
    <groupId>org.openpnp</groupId>
    <artifactId>opencv</artifactId>
    <version>3.2.0-1</version>
</dependency>

(and it looks like it occurs in all versions, I have tried all available in maven)

https://github.com/openpnp/opencv/issues/55

UPD.

so it is still required to load dlls explicitly. In my case

static {
        //System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
        System.load("D:\\Downloads\\opencv\\build\\java\\x64\\opencv_java2411.dll");
        System.load("D:\\Downloads\\opencv\\build\\x64\\vc12\\bin\\opencv_ffmpeg2411_64.dll");     
    }

explicit load of opencv_java and opencv_ffmpeg made the trick. Without loading opencv_ffmpeg explicitly the VideoCapture's .read(frame) was just always returning false with no any mention on any missing native ffmpeg dependency problem.

And the required java dependencies in pom.xml are:

    <dependency>
        <groupId>org.bytedeco.javacpp-presets</groupId>
        <artifactId>opencv</artifactId>
        <version>2.4.11-0.11</version>
    </dependency>
    <dependency>
        <groupId>org.openpnp</groupId>
        <artifactId>opencv</artifactId>
        <version>2.4.11-2</version>
    </dependency>

(please not i have downgraded the opencv version)