text: Video play issue from file using OpenCV library in QT
  Hi,
  Am new to OpenCV, trying to play video from file from Qt but unsuccessful.
  Following is the code am trying
  int VideoTest::Videoplay()
  {
  VideoCapture cap("/home/manu/Desktop/song.mp4"); if(!cap.isOpened()) // check if we succeeded return -1; Mat edges; namedWindow("edges",1); for(;;) { Mat frame; cap >> frame; cvtColor(frame, edges, COLOR_BGR2GRAY); GaussianBlur(edges, edges, Size(7,7), 1.5, 1.5); Canny(edges, edges, 0, 30, 3); imshow("edges", edges); if(waitKey(30) >= 0) break; } return 0;
  }
  Instead of file name if i give camera number am able to open camera and display it, But video file is not opening. Please help with the solution.
  - SGaist Lifetime Qt Champion
  Hi,
  That's not really a problem with Qt, you should check with the OpenCV folks. Note that I'm suspecting a missing codec since you are trying to read an .mp4 file.
  @SGaist Thanks for the response.
  i have installed ffmpeg, do i need to install codec as well? Am working on Ubuntu machine.
  I will post the issue in OpenCV forum.
  @Manohar_SL but you try to display video where? I not see qt widget in your code .... any how ... in witch opencv version you try? I std install of ubuntu 16 all codec you need is installed ..... so during opencv compile you can missing some option .... if you use cmake-gui these is simple to detect in advance to using make install command ... for exe. if not use OPTION QT .... not have opencv support for qt ....
  the code you show is only c++ ... so no qt windows appear when you run it? => no qt support in your opencv build.
  regards
  Giorgio
  @gfxx imshow("edges", edges); this will open mat frame and display i guess am not pro in opencv. opencv version am using is 2.4.9.
  @Manohar_SL said in Video play issue from file using OpenCV library in QT:
  this will open mat frame and display i guess am not pro in opencv. opencv version am using is 2.4.9.
  mmmm .... regarding qt-opencv, example of imgshow with only c++ code:
  example of imgshow c++ with qt support enable (the same piece of code):
  this to do well clear to me you've installed. What do you see when you cast your code? window with qt support or not?
  sorry these wath is means?:
  i guess am not pro in opencv
  regards
  Giorgio
  @gfxx Opencv installation is fine am able to load image using opencv and Qt and also am able to view my webcam example using opencv and Qt. opencv is working fine with Qt integration only problem am facing is with video display so sample code will be much appreciated.
  Regards
  Manu
  cooked and eaten ...... on Unthread ..... because if you use a desk application is better ... especially if it makes other things. I also use opengl to do the video render sometimes .....
  cv:Point ...bla bla cv::Mat ...bla bla using namespace cv; VideoCapture mo_cap; datathread::datathread (QObject *parent, bool bthw) : QThread(parent), Stop(bthw) { } datathread::~datathread() { this->Stop; mo_cap.release(); } cv::Point datathread::tMatrix1(0,0); cv::Point datathread::tMatrix2(90,640); cv::Point datathread::tMatrix3(480,0); cv::Point datathread::tMatrix4(480,640); cv::Mat datathread::dest_image100 = Mat::zeros(640, 480, CV_8UC3); cv::Mat datathread::temp_image = Mat::zeros(640, 480, CV_8UC1); int datathread::thExposure = 450; int datathread::thGain = 120; int datathread::MemoryRectSelect = 0; int datathread::SearchArea = 0; int datathread::RequestMbusSend = 0; bool datathread::RequestMbusUnlok = false; bool datathread::RequestKCCUnlok = false; bool datathread::RobotFirsTimeQuote = false; int datathread::Original_Exposure_Value = 160; void datathread::run() { cv::ocl::setUseOpenCL(true); std::ofstream tfile; if (!mo_cap.isOpened()) /** these because my camera take some time before become active **/ { qDebug() << "camera close"; // VideoCapture mo_cap; // open the default camer this->msleep(500); qDebug() << "camera initialized"; this->msleep(1000); qDebug() << "camera is opened?: " << mo_cap.open(0); /** now is more probable that the camere is active ... sometime it whitout these delay the thread run without camera than crash .... a common problem ...*/ } info = ("trasmission start...."); emit _msg(info); emit ok(); Size scaled (130,120); cvInitFont(&font, CV_FONT_HERSHEY_SIMPLEX, 1.0, 1.0); AR2 = areaprodotto + gapareaprodotto; AR1 = areaprodotto - gapareaprodotto; AR3 = areaprodotto; // int wKey = -1; selettorestringa = 0; selettoreriga1 = 0; selettoreriga2 = 0; controllokeypoint2 = 0; valorekeypoint2 = 0; s_p[0] = Point(0,0); s_p[1] = Point(0,640); s_p[2] = Point(480,0); s_p[3] = Point(480,640); /* img = cv2.imread('simple.jpg',0) // **** ORB EXAMPLE **** # Initiate STAR detector ****** img to ---> /home/opencv02/Immagini/dl_P.png orb = cv2.ORB() # find the keypoints with ORB kp = orb.detect(img,None) # compute the descriptors with ORB ## kp, des = orb.compute(img, kp) # draw only keypoints location,not size and orientation img2 = cv2.drawKeypoints(img,kp,color=(0,255,0), flags=0) plt.imshow(img2),plt.show()*/ //-----------------START-------------iterate through each frames of the video if (mo_cap.isOpened()) { do { QMutex mutex; // prevent other threads from changing the "Stop" value mutex.lock(); if(this->Stop) break; mutex.unlock(); if (thGain != ex_gain) /* ---------- these for manage camera parameter .... v4l issue for some of these .... on opencv forum my solutyon is posted ... but other post a better one .....*/ { thGain = ex_gain; mo_cap.set(CV_CAP_PROP_GAIN, thGain); } if (thExposure != ex_exposure_abs) { thExposure = ex_exposure_abs; mo_cap.set(CV_CAP_PROP_EXPOSURE, thExposure); /***** these not manage from v4l so you must use my correction (or other one) and install new v4l.cpp file *****/ } controlkeypoint2 = 0; mo_cap >> dest_image1111; //mo_cap.read(dest_image1111); //qDebug() << "errore 2 "; cvtColor(dest_image1111, dest_image1, COLOR_BGR2RGB); d_p[0] = tMatrix1; d_p[1] = tMatrix2; d_p[2] = tMatrix3; d_p[3] = tMatrix4; /*.................................... i use a series of image transformation .....*/ /*.... my horrible but very horrible code .....*/ Mat2QImage(dest_image1111); target.release(); /*** release all your matrix or cvMat .... than close do cicle....*/ } /** emit you signal **/ this->Stop; // this->msleep(700); // this->Stop; } void datathread::Mat2QImage(cv::Mat const& src) { if(!src.empty()) { cv::Mat temp; // make the same cv::Mat cvtColor(src, temp,CV_BGR2RGB); // cvtColor Makes a copt, that what i need QImage dest((const uchar *) temp.data, temp.cols, temp.rows, temp.step, QImage::Format_RGB888); dest.bits(); // enforce deep copy, see documentation emit _imma_orig(dest); } }