QCamera + QCameraViewfinder: how to mirror the the image displayed in the viewfinder?

Andy314

how can I get the QVideoRenderControl?
From the QViewFinder, which function, I find no.

Violet Giraffe

@SGaist, thanks. I, too, can't find a way to get it from QViewFinder (which is a QVideoWidget). Looks like I need QMediaService to get QVideoRenderControl from it.

SGaist

QMediaService *mediaService = viewFinder->mediaObject()->service();
QVideoRendererControl *rendererControl = mediaService->requestControl<QVideoRendererControl *>();
rendererControl->setSurface(myVideoSurface);

Don't forget to add the necessary checks.

Violet Giraffe

@SGaist
No such luck :( viewFinder->mediaObject() is nullptr.
IS there a restriction on when I should call mediaObject() relative to, say, show() or any other lifecycle-related method of the view finder?

SGaist

Did you set the viewFinder on the camera before calling mediaObject ?

Violet Giraffe

@SGaist
Nope, i was doing it just before that. So, now I put this code right after setViewfinder, and mediaService is not null, but mediaService->requestControl<QVideoRendererControl *>() returns nullptr.

SGaist

What OS are you running ? It might be that the backend doesn't provide that control.

Violet Giraffe

Windows 10.

nicesw123

how to mirror the the image displayed in the viewfinder?

+1

Actually
+1000

This is a very good question!
I also want to mirror the image (flip it left to right)!

PS:
I'm using Debian Testing, which requires these packages, to get QCamera working: qt5-default, libqt5multimedia5, libqt5multimedia5-plugins, libqt5multimediaquick-p5, libqt5multimediawidgets5, qml-module-qtmultimedia, qtmultimedia5-dbg, qtmultimedia5-dev

SGaist

Just a quick update:

    QVideoRendererControl *rendererControl = camera.service()->requestControl<QVideoRendererControl *>();
    if (rendererControl) {
        QAbstractVideoSurface *surface = rendererControl->surface();
        QVideoSurfaceFormat format = surface->surfaceFormat();
        format.setProperty("mirrored", true);

        surface->stop();
        surface->start(format);
    } else {
        qDebug() << "Backend doesn't provide a video renderer control";
    }

Violet Giraffe

Thanks, but still no. rendererControl is null, and I tried executing your snippet both before and after camera.start() call.

SGaist

Can you check what plugin is loaded ? It should be either the WMF or DirectX plugin. IIRC the DX plugin has the control.

Violet Giraffe

I can't see either. Here's the complete list of all the .dlls loaded.
I can, however, see an odd warning. I don't have a slightest idea if it's related, but probably not:

D3D11CreateDevice: Flags (0x2) were specified which require the D3D11 SDK Layers for Windows 10, but they are not present on the system.
These flags must be removed, or the Windows 10 SDK must be installed.
Flags include: D3D11_CREATE_DEVICE_DEBUG

SGaist

Sorry, I meant start your application with QT_DEBUG_PLUGINS set to 1.

Violet Giraffe

Is it an environment variable or a project define?

SGaist

Environment variable that you can set in the Run part of the Project panel.

Violet Giraffe

Here's the list. Can't see anything named WMF, but I guess I need to know the exact name to look for.

nicesw123

@Violet-Giraffe said:

Thanks, but still no. rendererControl is null

Same for Debian (and it's variants [Ubuntu, etc.])

nicesw123

Maby the way to do this for now...
(i.e. until the qt developers realize the value of extending QCameraImageProcessing or QCameraViewfinder to allow mirroring (flipping) the image)

...is to "derive from QAbstractVideoSurface" as shown here: http://doc.qt.io/qt-5/cameraoverview.html#viewfinder (find some example code there, showing rotation)

SGaist

DSEngine -> DirectShow. The plugin it self has the control but it seems it's not accessible yet.

If you are wiling to re-build the plugin, that can be modified.