How to write video file in OpenCV 2.4.3

Question

I am using OpenCV 2.4.3 to read and write a video file. My code is like this:

cv::VideoCapture video;
video.open ( "D:\\testVideo.avi" );
cv::VideoWriter output;
output.open ( "D:\\outputVideo.avi", CV_FOURCC('D','I','V','X'), 120, cv::Size ( 1200,1600), true );
cv::Mat img;

for ( int n = 0; ; n ++ )
{
     video >> img;
     output.write ( img );
 }

Then the result video was an empty file, and I couldn't open it. What did I do wrong here?

I'd say you're missing a call to something like `output.close()` — Herr von Wurst, Nov 29 '12 at 10:40
No, I tried similar methods as you suggested. It still didn't work. I doubt this could be a bug. — E_learner, Nov 30 '12 at 09:10
It is an unusaly high resolution though. Have you tried reducing it? — Herr von Wurst, Nov 30 '12 at 12:36
Not yet, because I really need this resolution, and it worked quite fine with 2.4.2 version before. — E_learner, Nov 30 '12 at 13:58
That's an important information. Then you should file a bug report. Can you not just go back to 2.4.2? — Herr von Wurst, Nov 30 '12 at 20:49
I really want to go back to 2.4.2, but the problem is, all the other codes I'm using are in 2.4.3, especially those GPU based functions. So I should sove it in this version. Thank you. — E_learner, Dec 03 '12 at 14:28

score 14 · Accepted Answer · answered Dec 01 '12 at 11:18

The problem might be the codec you are using.

A simple test to make sure your stuff is working properly is to simply retrieve frames from a webcam and write them on a video file:

// Load input video
cv::VideoCapture input_cap(argv[1]);
if (!input_cap.isOpened())
{
        std::cout << "!!! Input video could not be opened" << std::endl;
        return;
}

// Setup output video
cv::VideoWriter output_cap(argv[2], 
               input_cap.get(CV_CAP_PROP_FOURCC),
               input_cap.get(CV_CAP_PROP_FPS),
               cv::Size(input_cap.get(CV_CAP_PROP_FRAME_WIDTH),
               input_cap.get(CV_CAP_PROP_FRAME_HEIGHT)));

if (!output_cap.isOpened())
{
        std::cout << "!!! Output video could not be opened" << std::endl;
        return;
}


// Loop to read from input and write to output
cv::Mat frame;

while (true)
{       
    if (!input_cap.read(frame))             
        break;

    output_cap.write(frame);
}

input_cap.release();
output_cap.release();

The destructor of this class already calls release(). So when the variables are destroied, memory is freed automagically. — karlphillip, May 27 '13 at 14:44
Im trying using the default webcam and it always gives a result of `Output Video Could not be opened` Does the extension also matter? — Sohaib, Oct 03 '13 at 18:31

score 5 · Answer 2 · answered May 27 '13 at 11:14

5

You declare cv::VideoWriter output of frame size 1200*1600. So resize the frame to 1200*1600 using cv::resize(img,img,cv::Size(1200,1600));before output.write(img);

answered May 27 '13 at 11:14

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How to write video file in OpenCV 2.4.3

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