6

so there is OpenCV for Java now...! Can anyone tell me how to open Videofiles with it ?

I tryed and look all over the internet, but found nothing. The documentation of the VideoCapture class is not very helpfull, becaus it gives a C# example and show how to capture from a webcam.

the Q&A of OpenCV doesnt help either, because there is no (public) method to whom you can give a filename string.

BUT it should work as written in the API. But it doesn't There is however a privte method in the VideoCapture class with a sting parameter.

please answer if have a solution, or even if you have the same problem. garyee

UPDATE: (May 2017)

since Version 3.0.0 There is a constructor for the VideoCapture class that takes a string argument. So there is a easy solution to this Problem now!

4

4 回答 4

6

对我来说，为什么所谓的 opencv 自动生成的 java 包装器缺少此功能是一个谜。我首先使用 VideoCapture(String filename) 构造函数创建了一个新的 VideoCapture 类，并调用了私有本机方法。这会导致不满意的链接错误：

Exception in thread "main" java.lang.UnsatisfiedLinkError:       org.opencv.highgui.VideoCapture.n_VideoCapture(Ljava/lang/String;)J
    at org.opencv.highgui.VideoCapture.n_VideoCapture(Native Method)
    at org.opencv.highgui.VideoCapture.<init>(VideoCapture.java:90)
    at Tester.main(Tester.java:30)

这表明缺少相应的 JNIEXPORT。幸运的是，这可以修复。

令人惊讶的是，所需的 c-constructor 已在opencv-2.4.6/modules/highgui/include/opencv2/highgui/highgui.cpp 中定义

CV_WRAP VideoCapture(const string& filename);

我们在opencv-2.4.6/modules/java/generator/src/java/highgui+VideoCapture.java中的VideoCapture类中添加我们长的构造函数：

//
// C++: VideoCapture::VideoCapture(const string& filename)
//

// javadoc: VideoCapture::VideoCapture(String filename)
public VideoCapture(String filename)
{
    nativeObj = n_VideoCapture(filename);

    return;
}

关键而棘手的一步是添加 jni 导出。尤其是为 JNICALL 找到正确的方法名称被证明是具有挑战性的，因为构造函数被重载并且需要一个 java 类作为参数。此外，我们需要将 java 字符串转换为 c 字符串。其余部分是从其他构造函数中复制的。

在opencv-2.4.6/modules/java/generator/src/cpp/VideoCapture.cpp我们添加这个新的 JNIEXPORT：

//
//   VideoCapture::VideoCapture(const string& filename)
//

JNIEXPORT jlong JNICALL Java_org_opencv_highgui_VideoCapture_n_1VideoCapture__Ljava_lang_String_2
(JNIEnv* env, jclass, jstring filename);

JNIEXPORT jlong JNICALL Java_org_opencv_highgui_VideoCapture_n_1VideoCapture__Ljava_lang_String_2
(JNIEnv* env, jclass, jstring filename)
{
    try {
        LOGD("highgui::VideoCapture_n_1VideoCapture__Ljava_lang_String_2()");
        const char* jnamestr = env->GetStringUTFChars(filename, NULL);
        string stdFileName(jnamestr);
        VideoCapture* _retval_ = new VideoCapture( jnamestr );

        return (jlong) _retval_;
    } catch(cv::Exception e) {
        LOGD("highgui::VideoCapture_n_1VideoCapture__Ljava_lang_String_2() catched cv::Exception: %s", e.what());
        jclass je = env->FindClass("org/opencv/core/CvException");
        if(!je) je = env->FindClass("java/lang/Exception");
        env->ThrowNew(je, e.what());
        return 0;
    } catch (...) {
        LOGD("highgui::VideoCapture_n_1VideoCapture__Ljava_lang_String_2() catched unknown exception (...)");
        jclass je = env->FindClass("java/lang/Exception");
        env->ThrowNew(je, "Unknown exception in JNI code {highgui::VideoCapture_n_1VideoCapture__Ljava_lang_String_2()}");
        return 0;
    }
}

重新编译 OpenCV，它应该可以工作。

于 2013-10-10T07:16:29.007 回答
4

这是一个例子：

    public static void main(String[] args) {
    Mat frame = new Mat();
    VideoCapture camera = new VideoCapture("C:/Users/SAAD/Desktop/motion.mp4");
    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();

        }
    }
}`

如果您使用的是 Windows，请将 C:\opencv\build\x86\vc11\bin 添加到 Path 变量中

于 2014-09-10T14:07:13.803 回答
3

如果您使用的是新版本的 Java，这就是我让它工作的方式。

import org.opencv.core.*;
import org.opencv.videoio.*;

import java.awt.image.BufferedImage;
import java.awt.image.DataBufferByte;

import javax.swing.*;public class MainStruct {

public class MainStruct {

static { 
    try {
    System.load("C:opencv\\build\\x64\\vc14\\bin\\opencv_ffmpeg320_64.dll");
    } catch (UnsatisfiedLinkError e) {
        System.err.println("Native code library failed to load.\n" + e);
        System.exit(1);
    }
}

public static void main(String[] args)
{
    System.loadLibrary(Core.NATIVE_LIBRARY_NAME);

    //Create new MAT object
    Mat frame = new Mat();

    //Create new VideoCapture object
    VideoCapture camera = new VideoCapture("C:\\**VideoFileLocation**");

    //Create new JFrame object
    JFrame jframe = new JFrame("Video Title);

    //Inform jframe what to do in the event that you close the program
    jframe.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    //Create a new JLabel object vidpanel
    JLabel vidPanel = new JLabel();

    //assign vidPanel to jframe
    jframe.setContentPane(vidPanel);

    //set frame size
    jframe.setSize(2000, 4000);

    //make jframe visible
    jframe.setVisible(true);

    while (true) {
        //If next video frame is available
        if (camera.read(frame)) {
            //Create new image icon object and convert Mat to Buffered Image
            ImageIcon image = new ImageIcon(Mat2BufferedImage(frame));
            //Update the image in the vidPanel
            vidPanel.setIcon(image);
            //Update the vidPanel in the JFrame
            vidPanel.repaint();

        }
    }
}

public static BufferedImage Mat2BufferedImage(Mat m) {
    //Method converts a Mat to a Buffered Image
    int type = BufferedImage.TYPE_BYTE_GRAY;
     if ( m.channels() > 1 ) {
         type = BufferedImage.TYPE_3BYTE_BGR;
     }
     int bufferSize = m.channels()*m.cols()*m.rows();
     byte [] b = new byte[bufferSize];
     m.get(0,0,b); // get all the pixels
     BufferedImage image = new BufferedImage(m.cols(),m.rows(), type);
     final byte[] targetPixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
     System.arraycopy(b, 0, targetPixels, 0, b.length);  
     return image;
    }

}

于 2017-05-14T18:40:01.993 回答
2

这是它对我的工作方式。

VideoCapture capture=new VideoCapture();
capture.open("Vid.mp4");
Mat frame=new Mat();
            
   
for(;;){
   capture.read(frame); //reads captured frame into the Mat image
   imshow("Display",frame);
   if(cvWaitKey(30) >= 0) break;
}

于 2015-02-23T14:01:45.690 回答