视频关键帧提取，JAVA版

    import org.opencv.videoio.*;
    
    import java.io.File;
    import java.util.ArrayList;
    import java.util.List;
    
    import org.opencv.core.*;
    import org.opencv.imgcodecs.*;
    import org.opencv.imgproc.*;
    
    public class ExtractionVideoKeyFrames {
    	
    	Mat computeColorHist3D(Mat im, Size size)
    	{
    		Mat dst = new Mat(), hist = new Mat();
    		Imgproc.resize(im, dst, size, 0, 0, Imgproc.INTER_NEAREST);
    		Mat hsv_src = new Mat();
    		Imgproc.cvtColor(im, hsv_src, Imgproc.COLOR_BGR2HSV);
    //		Mat gray = new Mat(im.size(),CvType.CV_8UC1);
    //      Imgproc.cvtColor(im,gray,Imgproc.COLOR_RGB2GRAY);
    //		
    //		List images = new ArrayList();
    //      images.add(gray);
            
            List images=new ArrayList(3);
            images.add(hsv_src);
            //Core.split(hsv_src, images);
    
            MatOfInt channels= new MatOfInt(0);
            MatOfInt hSize = new MatOfInt(256);
            MatOfFloat ranges= new MatOfFloat(0,255);
            Imgproc.calcHist(images, channels, new Mat(), hist, hSize, ranges);
            //System.out.println(""+hist.rows()+","+hist.cols()+","+ hist.channels());
    		return hist;
    	}
    	
    	Mat computeColorHist(Mat im, Size size)
    	{
    		Mat dst = new Mat(), hist = new Mat();
    		Imgproc.resize(im, dst, size, 0, 0, Imgproc.INTER_NEAREST);
    		Mat gray = new Mat(im.size(),CvType.CV_8UC1);
            Imgproc.cvtColor(im,gray,Imgproc.COLOR_RGB2GRAY);
    		
    		List images = new ArrayList();
            images.add(gray);
    
            MatOfInt channels= new MatOfInt(0);
            MatOfInt hSize = new MatOfInt(128);
            MatOfFloat ranges= new MatOfFloat(0,128);
            Imgproc.calcHist(images, channels, new Mat(), hist, hSize, ranges);
    		return hist;
    	}
    	
    	double computeASE(Mat a, Mat b)
    	{		
    		double sumV = 1 - Imgproc.compareHist(a, b, 0);
    		return sumV;
    		
    //		Mat dst = new Mat();
    //		Core.absdiff(a, b, dst);
    //
    //		Scalar sumV = Core.sumElems(dst);
    //		return sumV.val[0];
    	}
    	
    	int ExtractKeyframes(String videoPath, double rate, String outImgPath){
    		VideoCapture cap = new VideoCapture();
    		System.out.println(cap.isOpened());
    		if (!cap.open(videoPath)) {
    			
    			System.out.println("Open video file error!");
    			return -1;
    		}
    		
    		File file = new File(outImgPath);  
    		if(!file.exists()){  
    		    file.mkdirs();  
    		} 
    		
    		int width = (int)cap.get(Videoio.CV_CAP_PROP_FRAME_WIDTH);
    		int height = (int)cap.get(Videoio.CV_CAP_PROP_FRAME_HEIGHT);
    		float fps = (float)cap.get(Videoio.CV_CAP_PROP_FPS);
    		int nframes = (int)cap.get(Videoio.CV_CAP_PROP_FRAME_COUNT);
    		System.out.println("W:"+width+";H:"+height+";FPS:"+fps+";N:"+nframes);
    		
    		int nscale = 1;
    
    		if (width%4==0 && height%4==0)
    			nscale = 4;
    		else if (width%2==0 && height%2==0)
    			nscale = 2;
    		Size size = new Size(width/nscale, height/nscale);
    		//double fnorm = size.area() * 2;
    		
    		Mat frame = new Mat();
    		Mat lastFrame = new Mat();
    		Mat histA = new Mat();
    		Mat histB = new Mat();
    		long nCount = 0;
    		int frameID = 1; int lastFrameID = 1;
    		double tic = (double)Core.getTickCount();
    		while (cap.read(frame))
    		{
    			if (frame.empty()){
    				break;
    			}
    
    			if (lastFrameID==1)
    			{
    				frameID = (int)cap.get(Videoio.CV_CAP_PROP_POS_FRAMES);
    				lastFrameID = frameID;
    				frame.copyTo(lastFrame);
    				continue;
    			}
    
    			if (++nCount % 15 != 0) continue;	// Processing one frame in each second
    
    			frameID = (int)cap.get(Videoio.CV_CAP_PROP_POS_FRAMES);
    
    			histA = computeColorHist3D(frame, size);
    
    			double aseV = rate;
    			if (histB.empty())
    				System.out.println(aseV);
    			else{
    				aseV = computeASE(histA, histB);
    				System.out.println(aseV);
    			}
    
    			if (aseV >= rate) {
    				String imagePath = outImgPath+"/"+lastFrameID+".jpg";
    				if (!Imgcodecs.imwrite(imagePath, lastFrame))
    					return -2;
    				//if(g_OnSavedKeyFrame != NULL) {
    					//sprintf(imagePath,"%d.jpg", lastFrameID);
    					//g_OnSavedKeyFrame(inVidPath, imagePath, (int)(lastFrameID/fps),(int)((frameID-lastFrameID)/fps), g_User, g_Data);
    				//}
    				lastFrameID = frameID;
    				frame.copyTo(lastFrame);
    			}
    
    			histA.copyTo(histB);		
    		}
    
    		if (!lastFrame.empty())
    		{
    			//char imagePath[1024];
    			String imagePath=outImgPath+"/"+ lastFrameID+".jpg";
    			if (!Imgcodecs.imwrite(imagePath, lastFrame))
    				return -2;
    			//if(g_OnSavedKeyFrame != NULL) {
    			//	sprintf(imagePath,"%d.jpg", lastFrameID);
    			//	g_OnSavedKeyFrame(inVidPath, imagePath, (int)(lastFrameID/fps),(int)((frameID-lastFrameID)/fps), g_User, g_Data);
    			//}
    		}
    		System.out.println("NFRAMES(in reality)="+nCount);	
    
    		double toc = (double)Core.getTickCount();
    		System.out.println("ELAPSED TIME="+(toc-tic)/Core.getTickFrequency());
    		return 0;
    	}
    	
    	public static void main(String[] args) {
    		// TODO Auto-generated method stub
    		//Runtime.getRuntime().load("/boaplaust/libopencv_java340.so");
    		System.loadLibrary(Core.NATIVE_LIBRARY_NAME);
    		ExtractionVideoKeyFrames evf = new ExtractionVideoKeyFrames();
    		evf.ExtractKeyframes("E:/720P.flv",0.5,"E:/VideosOutput/");
    	}
    
    }