windows phone 8.1 RT Zxing.net implementation : issue with CapturePhotoToStreamAsync

Question

I'm using ZXing.net to create a UserControl for scanning barcode into a Windows Phone 8.1 RT app using the camera.

The barcode are decoded well but i'm having freezes on the UI when the method CapturePhotoToStreamAsync is called, even it is awaited. It takes about 600 ms to execute.

I'm testing the app into the emulator.

The code below is executed in an async method :

// Preview of the camera    
await _mediaCapture.InitializeAsync(settings);
VideoCapture.Source = _mediaCapture;
VideoCapture.FlowDirection = Windows.UI.Xaml.FlowDirection.LeftToRight;
await _mediaCapture.StartPreviewAsync();

VideoEncodingProperties res = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties;
ImageEncodingProperties iep = ImageEncodingProperties.CreateBmp();

iep.Height = res.Height;
iep.Width = res.Width;

var barcodeReader = new BarcodeReader
{
     TryHarder = true,
     AutoRotate = true
};

WriteableBitmap wB = new WriteableBitmap((int)res.Width, (int)res.Height);
while (_result == null)
{
     using (var stream = new InMemoryRandomAccessStream())
     {
        await _mediaCapture.CapturePhotoToStreamAsync(iep, stream);

        stream.Seek(0);
        await wB.SetSourceAsync(stream);

        _result = barcodeReader.Decode(wB);
      }
 }

 await _mediaCapture.StopPreviewAsync();
 //callback to handle result
 ScanCallback(_result.Text);

What can I do to prevent the UI from freezing ?

Answer 1

Luckily you don't have to capture photo to decode QRCode/Barcode on Windows Phone 8.1 Runtime. It is a quite new solution actually, but it works: https://github.com/mmaitre314/VideoEffect#realtime-video-analysis-and-qr-code-detection After istalling the nuget package, you can easily decode barcodes realtime, without the need of calling CapturePhotoToStreamAsync. The only drawback is that you can only target ARM. You can find the sample code on the site. Or you can contact me, and I can send you the part of my project where I use this.