QR with Zxing and Vuforia

Use Vuforia's callbacks to handle setting up pixel frame format:

 using System;
 using UnityEngine;
 using UnityEngine.UI;
 
 using Vuforia;
 using static Vuforia.Image;
 using ZXing;
 using static ZXing.RGBLuminanceSource;
 
 public class MainRuntimeBehaviour : MonoBehaviour
 {
     #region Variables
 
     [SerializeField, Tooltip("Text UI Element to show seconds passed.")]
     /// <summary>
     /// Text UI Element to show seconds passed.
     /// </summary>
     private Text secondsPassedText = null;
 
     [SerializeField, Tooltip("Text UI Element to show the decoded text.")]
     /// <summary>
     /// Text UI Element to show the decoded text.
     /// </summary>
     private Text scannedText = null;
 
     [SerializeField, Tooltip("The RawImage to display the camera feed in.")]
     /// <summary>
     /// The RawImage to display the camera feed in.
     /// </summary>
     private RawImage cameraFeed = null;
 
     [SerializeField, Tooltip("Pixel Format supplied to Vuforia's Camera API.")]
     /// <summary>
     /// Image Frame Format supplied to Vuforia's Camera API.
     /// </summary>
     private PIXEL_FORMAT pixelFormat = PIXEL_FORMAT.RGBA8888;
 
     /// <summary>
     /// Barcode reader instance used for decoding QR codes.
     /// </summary>
     private IBarcodeReader barcodeReader;
 
     /// <summary>
     /// Time elapsed in seconds, displayed on screen.
     /// </summary>
     private double secondsPassed = 0f;
 
     /// <summary>
     /// Set whenever the application is active.
     /// </summary>
     private bool frameFormatRegistered = false;
 
     #endregion
 
 
     #region MonoBehaviour Callbacks
     
     /// <summary>
     /// Called before any MonoBehaviour Start callbacks.
     /// </summary>
     private void Awake()
     {
         // Disable logging when in build
 #if UNITY_EDITOR
         Debug.unityLogger.logEnabled = true;
 #else
         Debug.unityLogger.logEnabled = false;
 #endif
 
         barcodeReader = new BarcodeReader();
         VuforiaARController.Instance.RegisterVuforiaStartedCallback(OnVuforiaStart);
         VuforiaARController.Instance.RegisterTrackablesUpdatedCallback(OnTrackablesUpdate);
         VuforiaARController.Instance.RegisterBackgroundTextureChangedCallback(OnBackgroundTextureChange);
         VuforiaARController.Instance.RegisterOnPauseCallback(OnPause);
     }
 
     /// <summary>
     /// Run when this MonoBehaviour is destroyed. Useful for unregistering callbacks or disposing native handles. 
     /// </summary>
     private void OnDestroy()
     {
         VuforiaARController.Instance.UnregisterVuforiaStartedCallback(OnVuforiaStart);
         VuforiaARController.Instance.UnregisterTrackablesUpdatedCallback(OnTrackablesUpdate);
         VuforiaARController.Instance.UnregisterBackgroundTextureChangedCallback(OnBackgroundTextureChange);
         VuforiaARController.Instance.UnregisterOnPauseCallback(OnPause);
     }
 
     /// <summary>
     /// MonoBehaviour callback for processing GUI in Unity
     /// </summary>
     private void OnGUI()
     {
         // show how much time passed
         secondsPassed += Time.deltaTime;
         secondsPassedText.text = $"{secondsPassed,-1:F2}s";
     }
 
     #endregion
 
 
     #region Vuforia Callbacks
 
     /// <summary>
     /// Run when Vuforia is initialised.
     /// </summary>
     private void OnVuforiaStart()
     {
         // Run the registration for the first time
         RegisterFrameFormat();
     }
 
     /// <summary>
     /// Run when changes in trackable objects are detected.
     /// </summary>
     private void OnTrackablesUpdate()
     {
         // only attempt to capture camera feed frames if pixel format was recognised
         if (frameFormatRegistered)
         {
             var cameraFeedFrame = CameraDevice.Instance.GetCameraImage(pixelFormat);
             if (cameraFeedFrame != null)
             {
                 Debug.Log($@"IMAGE DETAILS
                 Format:      {cameraFeedFrame.PixelFormat}
                 Size:        {cameraFeedFrame.Width}x{cameraFeedFrame.Height}
                 Buffer Size: {cameraFeedFrame.BufferWidth}x{cameraFeedFrame.BufferHeight}
                 Stride:      {cameraFeedFrame.Stride}");
 
                 ReadQRCode(cameraFeedFrame);
             }
         }
     }
 
     /// <summary>
     /// Run when the background texture changes. Useful for reading camera feeds.
     /// </summary>
     private void OnBackgroundTextureChange()
     {
         var videoTextureInfo = VuforiaRenderer.Instance.GetVideoTextureInfo();
         Debug.Log($@"OnBackgroundTextureChange() called with:
                   Image Size:   {videoTextureInfo.imageSize.x}x{videoTextureInfo.imageSize.y}
                   Texture Size: {videoTextureInfo.textureSize.x}x{videoTextureInfo.textureSize.y}");
 
         // If the video background texture is changed, reassign to the camera feed texture
         cameraFeed.texture = VuforiaRenderer.Instance.VideoBackgroundTexture;
     }
 
     /// <summary>
     /// Run when the application is paused from the system.
     /// </summary>
     /// <param name="paused">Whether the application has been paused or not. Supplied by the system.</param>
     private void OnPause(bool paused)
     {
         if (paused)
         {
             Debug.Log("App was paused.");
             UnregisterFrameFormat();
         }
         else
         {
             Debug.Log("App was resumed.");
             RegisterFrameFormat();
         }
     }
 
     /// <summary>
     /// Register the pixel format to be used for camera feed frames.
     /// </summary>
     private void RegisterFrameFormat()
     {
         if (frameFormatRegistered = CameraDevice.Instance.SetFrameFormat(pixelFormat, true))
         {
             Debug.Log($"Registered pixel format {pixelFormat}.");
         }
         else
         {
             Debug.LogError($@"Pixel format {pixelFormat} could not be registered.
             The format may not be supported by your device.
             Consider using a different pixel format.");
         }
     }
 
     /// <summary>
     /// Unregister the assigned pixel format.
     /// </summary>
     private void UnregisterFrameFormat()
     {
         Debug.Log($"Unregistering camera pixel format {pixelFormat}.");
         CameraDevice.Instance.SetFrameFormat(pixelFormat, false);
         // Ensure that the feed is not captured if the application is paused
         frameFormatRegistered = false;
     }
 
     #endregion
 
 
     #region Helper Methods
 
     /// <summary>
     /// Decode any single QR code present in a camera frame.
     /// </summary>
     /// <param name="image">The camera feed frame.</param>
     private void ReadQRCode(Vuforia.Image image)
     {
         if (image == null || image.Pixels == null)
         {
             return;
         }
 
         try
         {
             // decode the current frame
             var result = barcodeReader.Decode(image.Pixels, image.BufferWidth, image.BufferHeight, VuforiaToZXingBitmapFormat(pixelFormat));
             if (result != null)
             {
                 scannedText.text = result.Text;
                 Debug.Log($"Decoded {result.Text}");
             }
             else
             {
                 Debug.Log("Nothing decoded yet.");
             }
         }
         catch (Exception e)
         {
             Debug.LogError(e.Message);
         }
     }
 
     /// <summary>
     /// Map Vuforia's PIXEL_FORMAT enumeration to ZXing's BitmapFormat enumeration wherever applicable.
     /// </summary>
     /// <param name="vuforiaFormat">The pixel format set in the inspector.</param>
     /// <returns>The corresponding BitmapFormat value.</returns>
     private static BitmapFormat VuforiaToZXingBitmapFormat(PIXEL_FORMAT vuforiaFormat)
     {
         switch (vuforiaFormat)
         {
             case PIXEL_FORMAT.GRAYSCALE:
                 return BitmapFormat.Gray8;
             case PIXEL_FORMAT.RGB888:
                 return BitmapFormat.RGB24;
             case PIXEL_FORMAT.RGBA8888:
                 return BitmapFormat.RGBA32;
             case PIXEL_FORMAT.RGB565:
                 return BitmapFormat.RGB565;
             default:
                 Debug.LogError($"Vuforia {vuforiaFormat} does not have a corresponding ZXing BitmapFormat type. Please use another format type.");
                 return BitmapFormat.Unknown;
         }
     }
 
     #endregion
 }