System information:

• NVIDIA Jetson Xavier NX (aarch64)
• Qt 5.15 (qmake)
• Cross compilaton using Qt Creator on Ubuntu 22.04

Problem Description:
I am using the Camera & VideoOutput QML components (https://doc.qt.io/qt-5/qml-qtmultimedia-camera.html & https://doc.qt.io/qt-5/qml-qtmultimedia-videooutput.html) together with a v4l2loopback device. I use this device as a sink in my GStreamer pipeline (v4l2sink) and as a source for the Camera QML component. Every few seconds I get this message:
CameraBin error: "Failed to allocate a buffer"

This is a block diagram of my GStreamer pipeline:

The video that is streamed into the v4l2sink is captured using the Camera QML component.
This is the code for the Camera QML component (the QML component Loader – named liveViewLoader – is not included in this code snippet as this is not relevant for the issue in my opinion):

import QtQuick 2.0
import QtMultimedia 5.15

Item
{
    /*
     * If the video stream does not exist on creation, the camera will never work.
     * The Component + Loader circumvents this by reloading the camera components after a timeout has occured.
     * The video device itself has to exist before the start, though.
     */
    id:             wrappingItem
    anchors.fill:   parent

    property string videoDeviceFile: "/dev/video2"
    Timer
    {
        id:         cameraTimeoutTimer
        interval:   1000 /* in ms */
        running:    false
        repeat:     false
        onTriggered:
        {
            liveViewLoader.restart();
        }
    }

    Component
    {
        id: liveViewComponent
        Item
        {
            height: wrappingItem.height
            width:  wrappingItem.width

            id: liveViewComponentItem

            Camera
            {
                id:             camera
                captureMode:    Camera.CaptureStillImage
                deviceId:       wrappingItem.videoDeviceFile
                onCameraStatusChanged:
                {
                    console.log("Live view camera state changed to", camera.cameraStatus)
                    var liveViewRunning = (camera.cameraStatus == Camera.ActiveStatus);
                    // If the camera changed state, but it's not running, set a timeout to restart the camera via the Loader.
                    cameraTimeoutTimer.start();
                    if ( liveViewRunning )
                    {
                        cameraTimeoutTimer.stop();
                    }
                }

                Component.onCompleted:
                {
                    checkAndHandleCameraAvailability();
                }
            }

            VideoOutput
            {
                id:             videoOutputArea
                source:         camera
                anchors.fill:   parent
                flushMode:      VideoOutput.EmptyFrame
                focus:          visible
            }

            function checkAndHandleCameraAvailability()
            {
                // If the selected camera is not available, the camera will automatically select a different camera that's available on the system. This is a workaround to disable that behavior.
                camera.deviceId = wrappingItem.videoDeviceFile

                let videoDeviceIsAvailable = (camera.deviceId === wrappingItem.videoDeviceFile);
                if (videoDeviceIsAvailable)
                    return;

                console.log("Camera is currently using video device", camera.deviceId)
                console.log("AvlStreamHandler.videoDeviceFile: ", AvlStreamHandler.videoDeviceFile)
                console.log("Video device", wrappingItem.videoDeviceFile, "is not available.")
                liveViewLoader.stop();
            }
        }
    }
}

Question:
Can anyone give me a hint why I get the “CameraBin error: “Failed to allocate a buffer”” error message and how this error could possibly be resolved?

Best regards

B0bbyR4y