如何同时在不同的QT小部件上显示多个视频

Question

I have done a code which run different algorithms of OpenCV on different QWidgets .. so I have 3 tabs and each should show a camera live streaming with the processing of them .. I take the capture of the video at the first tab widget and pass it by global reference to the other tabs... however I get this problem

libv4l1: error setting pixformat: Device or resource busy
HIGHGUI ERROR: libv4l unable to ioctl VIDIOCSPICT

although I have only one capture ..

any ideas?

Answer 1

The proper way to handle this issue is copy the frame retrieved by the camera and make it available to the other tabs. Do not share the capture interface!

Answer 2

I'm also working with OpenCV and Qt. For emulating a camera I'm using the Capture object to read frames from a video file and send them over TCP/IP.

To make your frames available to all the others widgets I suggest to you to create a new class that inherits from QIODevice, initialize your capture device. Every time you get a new frame from the camera, you save the data into a QByteArray variable and emits the readyRead() signal.

Note: - all your widgets have to be connected to the readyRead() signal - once you get a new frame, remember to clean previous data - you have to re-implement function virtual qint64 readData( char * data, qint64 maxSize ) to be able to read your data

Something like this

#include "opencv2/highgui/highgui.hpp"

using namespace cv;

class VideoCaptureDevice : public QIODevice
{
    Q_OBJECT

public:
    VideoCaptureDevice(QObject *parent);
    virtual ~VideoCaptureDevice();

private:
    VideoCapture            m_capture;
    QByteArray      m_receivedData;

protected:
    // from QIODevice
    qint64 writeData(const char * data, qint64 maxSize);
    qint64 readData(char * data, qint64 maxSize);

};