video doesn't display on LCD screen

SGaist

How are you feeding your pipeline ?

Jeffff

Seems that I cannot upload my source code here. It is pretty simple, first I use opencv to capture a image, and emit the frame.

    forever{
        try {
            if (!normal_video.isOpened()) {
                continue;
            }
            cv::Mat normal_frame;
            normal_video >> normal_frame;
            emit updateCameraFrame(normal_frame.clone());
        }

Then in another thread, the frame is handled:

void VideoManager::frameReceived(const cv::Mat &frame) {
    if(mRunning){
        cv::Mat image(frame);
        mCameraProducer->updateFrame(Mat2QImage(image));
    }
}
......
void VideoProducer::updateFrame(QImage image)
{
    if(image.size() != mFormat.frameSize())
    {
        qDebug() << "newSize: " << image.size();
        closeSurface();
        mFormat = QVideoSurfaceFormat( image.size(), QVideoFrame::PixelFormat::Format_RGB32);
        mSurface->start(mFormat);
    }
    mSurface->present( QVideoFrame( image ) );
}

As shown above, everything is working unless last step: mSurface->present(), which cannot really present the image/video on screen.

SGaist

@Jeffff said in video doesn't display on LCD screen:

VideoProducer

Is that one in a different thread than the main thread ?

Jeffff

Yes, sure. video capturing and displaying are 2 different threads, they are sync by signal.

SGaist

That I understood, my question is: does the displaying happen in the main thread of your application ? Not a secondary thread that you created.

Jeffff

Yes, it is the main thread of my application. As I've mentioned at the beginning, the same code can run on my Ubuntu.

SGaist

@Jeffff said in video doesn't display on LCD screen:

multimedia.video: media object is QObject(0x0)

This one looks pretty odd and is likely related to your 0 frame rate.

Can you test with a minimal QVideoWidget to compare ?

Jeffff

I did some test by qmlvideo sample App, which runs good on same imx6 board. As qmlvideo runs smoothly, it means my running environment is good.
On the other hand, I found that if I use small resolution image frame(such as 480*270), it is working. All frames are display on preset windows(800*480), obviously, it should be gstreamer which enlarges the frame. The very weird thing is that other large resolutions, such as (640*360, 1280*720, 1920*1080), are not OK to be displayed, in replace, the area keeps dark.
With the logging enabled , I can also find the gstreamer plugin inserted as below figure shows even though video cannot be displayed.

Jeffff

For my own app and the qmlvideo app, I also dump their lib dependency as below:

file:///mnt/hgfs/Share/Screenshot%20from%202021-12-01%2023-30-58.png
Another strange part to me: the Qt5Multimediea appears in my app, while it doesn't appear in qmlvideo example. As I described before, my app cannot display video frame, while qmlvideo can display...

SGaist

@Jeffff said in video doesn't display on LCD screen:

qmlvideo

Can you give a link to that example ?

Jeffff

@SGaist
Sorry I cannot get your idea.
The link here guides me to get the "qmlvideo" app. I havn't change any code of this app, it should be the original sample code of using QtMultimedia.

SGaist

Ok, the sample does not link to the QtMultimedia library directly because it does not use it directly as is your C++ application.

The QVideoWidget class, if memory serves well does not support the same number of formats as the QtQuick Video item.