QCamera black screen or turns off
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Hello,
I know there are already a lot of posts about Qmultimedia and black screens, but I can't find a solution for my problem. I'm using Qt5.13.0.
I try to make a simple application with QCamera.
This is the code:#include <QApplication> #include <QCamera> #include <QCameraViewfinder> #include <QCameraInfo> int main(int argc, char *argv[]) { QApplication app(argc, argv); QCamera camera; QCameraViewfinder viewfinder; viewfinder.show(); camera.setViewfinder(&viewfinder); camera.start(); qDebug() << "error: " <<camera.error() << "\n state:" << camera.state() << "\n status: " << camera.status() << "\n errorstring: " << camera.errorString() << "\n camptureMode: " << camera.captureMode() << "\n camera.lockStatus: " << camera.lockStatus() << "\n availableMetaData: " << camera.availableMetaData(); return app.exec(); }When I run the program, I only get a black screen, but no error message (see screenshot with debug-info).
It seems to me that the camera is not switched on.
Then I tried to run the .exe-File (camera_simple.exe) without QCreator. Interestingly, I get a picture and the camera works for about 5 seconds. Then the picture freezes and the camera turns off (green light next to the camera is gone).What is wrong?
Thanks for your help.
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Hi,
thanks for your answer.I tried to follow the QCamera example and so I changed my code. The result is the same (still black screen). I have only one camera (laptop internal camera).
Code:int main(int argc, char *argv[]) { QApplication app(argc, argv); QCamera *camera; const QList<QCameraInfo> cameras = QCameraInfo::availableCameras(); for (const QCameraInfo &cameraInfo : cameras) { qDebug() << "cameraInfo.deviceName: "<< cameraInfo.deviceName(); camera = new QCamera(cameraInfo); } QCameraViewfinder viewfinder; viewfinder.show(); camera->setViewfinder(&viewfinder); camera->start(); qDebug() << "error: " <<camera->error() << "\n state:" << camera->state() << "\n status: " << camera->status() << "\n errorstring: " << camera->errorString() << "\n camptureMode: " << camera->captureMode() << "\n camera.lockStatus: " << camera->lockStatus() << "\n availableMetaData: " << camera->availableMetaData() << "\n camera.isAvailable: " << camera->isAvailable() << "\n viewfinder.isEnabled: "<< viewfinder.isEnabled() << "\n viewfinder.isVisible: " <<viewfinder.isVisible(); return app.exec(); }debug-information:
cameraInfo.deviceName: "@device:pnp:\\\\?\\usb#vid_04f2&pid_b5c0&mi_00#6&34052049&0&0000#{65e8773d-8f56-11d0-a3b9-00a0c9223196}\\global" error: QCamera::NoError state: QCamera::ActiveState status: QCamera::ActiveStatus errorstring: "" camptureMode: QFlags(0x1) camera.lockStatus: QCamera::Unlocked availableMetaData: () camera.isAvailable: true viewfinder.isEnabled: true viewfinder.isVisible: true -
Are you on Windows ?
By the way, did you try a more recent version of Qt ? -
What kind of camera is that ?
Do you have it working properly with e.g. VLC ?
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This code is working perfectly in Qt 5.12.0.
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Thanks for your answers and your help.
I'm using the internal camera of a Lenovo T470.
VLC - I did not test ist. But meanwhile I installed gstreamer 1.0 and everything was working fine.After that I found out that there is a common known problem with Lenovo-laptops and the camera. I found the solution (adding two values in the regedit) and no it's working fine.
