QML Camera error

B0bbyR4y

Hi,

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