Reading a video with openCV

问题

I have a video engine2.avi that I want to read and show with openCV. Here's my code:

#include <opencv2/core/core.hpp>
#include <opencv2/highgui/highgui.hpp>
#include <iostream>

using namespace cv;

int main(int argc, char** argv)
{
    string filename = "D:\\BMDvideos\\engine2.avi";
    VideoCapture capture(filename);
    Mat frame;

    if( !capture.isOpened() )
        throw "Error when reading steam_avi";

    namedWindow("w", 1);
    for( ; ; )
    {
        capture >> frame;
        //if(!frame)
        //    break;
        imshow("w", frame);
        waitKey(20); // waits to display frame
    }
    waitKey(0);
}

This code doesn't work if my file has the codec YUV 4:2:2 (UYVY) (I recorded the video using Direct-Show), but works when I use a video I grabbed whit openCV !!

Has anybody an Idea how this could work ?

UPDATE:

After reading some links, suggesting that catching exception will solve the problem, I modified my code. It didn't help, but here is the modified code:

cv::VideoCapture cap("d:\\BMDvideos\\engine2.avi");
cv::Mat frame;

try
{
    cap >> frame;
}
catch(cv::Exception ex)
{
    std::cout << ex.what() << std::endl;
}
catch(...)
{
    std::cout << "Unknown exception" << std::endl;  
}

The program crashes in cap>>frame. I readed similar questions but they use a frame in YUV (4:2:0), while my video has UYVY (4:2:2). How can I convert this into RGB color model?

UPDATE 2:

After karlphillip's suggestion, I used OpenCV2.4.3, but I still got the same error using the code below:

#include <opencv2\core\core.hpp>
#include <opencv2\highgui\highgui.hpp>
#include <opencv2\opencv.hpp>
using namespace cv;
using namespace std;

int main(){
    cv::Mat frame;
    cv::VideoCapture cap("d:\\BMDvideos\\B\\Aufnahme.avi");
    if(!cap.isOpened())
    {
        cout << "Error can't find the file"<<endl;
    }

    while(1){
        if(!cap.read(frame))
            imshow("",frame);

        cv::waitKey(33);
    }
    return 0;
}

回答1:

Here is a couple of links that might help you:

• Load, Save and Show YUV 420 images
• How to read a frame from YUV file in OpenCV?
• Converting YUV into BGR or RGB in OpenCV

Edit:

I must clear something first: OpenCV is capable of reading YUV frames from a video file because it's the underlying library (FFmpeg/GStreamer) that does the job. OpenCV also supports converting between a specific type of YUV and RGB through cvCvtColor() with CV_YCrCb2RGB or CV_RGBYCrCb.

Upon examining your question again, I noticed you didn't specify the kind of error that happened. You could do a better job at dealing with a possible failure from the capture interface by printing a message to the screen instead of throwing it.

I tested the video file you shared and I had no problems playing it on a window using the following code:

#include <cv.h>
#include <highgui.h>

#include <iostream>

int main(int argc, char* argv[])
{
    cv::VideoCapture cap(argv[1]);
    if (!cap.isOpened())
    {
        std::cout << "!!! Failed to open file: " << argv[1] << std::endl;
        return -1;
    }

    cv::Mat frame;
    for(;;)
    {

        if (!cap.read(frame))             
            break;

        cv::imshow("window", frame);

        char key = cvWaitKey(10);
        if (key == 27) // ESC
            break;
    }

    return 0;
}

If, for some reason, the capture interface fails to open the file it will quit the application immediately, instead of going further just to crash at cap.read(frame).

回答2:

If you are just looking out for displaying the video, here's the code that worked for me, Please check if it helps you in any way.

#include <stdio.h>
#include <opencv2/opencv.hpp>
int main(){
CvCapture *camera=cvCaptureFromFile("C:\\test.avi");
if (camera==NULL)
    printf("camera is null\n");
else
    printf("camera is not null");

cvNamedWindow("img");
while (cvWaitKey(10)!=atoi("q")){
    double t1=(double)cvGetTickCount();
    IplImage *img=cvQueryFrame(camera);
    /*if(img){
        cvSaveImage("C:/opencv.jpg",img);
    }*/
    double t2=(double)cvGetTickCount();
    printf("time: %gms  fps: %.2g\n",(t2-t1)/(cvGetTickFrequency()*1000.), 1000./((t2-t1)/(cvGetTickFrequency()*1000.)));
    cvShowImage("img",img);
}
cvReleaseCapture(&camera);
}

Hope this helps you.

回答3:

I realised that, the VideoCapture object needs opencv_ffmpeg310_64.dll. Once you copy this dll in your binary folder your VideoCapture object should be able to read video file.

来源：https://stackoverflow.com/questions/14833553/reading-a-video-with-opencv