Qt6 QML Multimedia: How to crop video played from MediaPlayer to VideoOutput

[rklemm]

I am streaming to a Qt app from an RTSP server that sends horizontally tiled 1080p video (so the incoming video has a raw size of 3840x1080). I want to be able to crop to either the left or right half of the video from QML. Currently, I have this code - it works, but it feels like I am overcomplicating it:

 MediaPlayer {
        id: mediaplayer
        // Sends 3840x1080 video which is a tiled 1080p stream
        source: "rtsp://xxxxx"
        videoOutput: videoOut
}

// Hide a 3840x1080 VideoOutput behind a Shader widget that crops it
StackLayout {
        anchors.fill: parent
        currentIndex: 1

        VideoOutput {
                id: videoOut
        }

        ShaderEffectSource {
                id: cropVideo
                property bool viewLeft: true
                sourceItem: videoOut
                hideSource: true
                live: true

                Layout.maximumHeight: 1080
                Layout.maximumWidth: 1920
                Layout.preferredHeight: 1080
                Layout.preferredWidth: 1920

                sourceRect: viewLeft ? Qt.rect(0, 0, 1920, 1080) 
                                    : Qt.rect(1920, 0, 1920, 1080)
        }
}

It feels like there should be a way to crop the video directly from either the MediaPlayer or VideoOutput widgets.

[GrecKo]

VideoOutput has a sourceRect property.

[rklemm]

@GrecKo It does, but it seems to be a read-only reflection of the viewport set for the video frame objects that are coming through the videoSink. When I attempt to assign to it, I get the QML error: Invalid property assignment: "sourceRect" is a read-only property. The docs do not appear to reflect the fact that sourceRect is read-only. I am using Qt 6.3.

Looking at the source for VideoOutput (https://github.com/qt/qtmultimedia/blob/37c2d097eb5dd8671cc752dc920da11d66105905/src/multimediaquick/qquickvideooutput_p.h#L41), we can see that the Q_PROPERTY for sourceRect is read-only in both the 6.3 and dev branches.

I have had the thought of attempting to manually set the viewport of the QVideoFrameFormat of the frames coming through the VideoOutput's videoSink, but I haven't created a working solution for that strategy yet.