使用detectFacesAsync进行API面部识别Microsoft认知服务C＃

Question

我有一个问题我不能使用DetectFacesAsync来检测我从我的电脑网络摄像头获得的预览中的面部。你能帮帮我吗？

private async Task GetPreviewFrameAsSoftwareBitmapAsync()
{
    var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties;
    var videoFrame = new VideoFrame(BitmapPixelFormat.Bgra8, (int)previewProperties.Width, (int)previewProperties.Height);
    using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync(videoFrame))
    {
        SoftwareBitmap previewFrame = currentFrame.SoftwareBitmap;
        FrameInfoTextBlock.Text = String.Format("{0}x{1} {2}", previewFrame.PixelWidth, previewFrame.PixelHeight, previewFrame.BitmapPixelFormat);

        if (ShowFrameCheckBox.IsChecked == true)
        {
            var sbSource = new SoftwareBitmapSource();
            await sbSource.SetBitmapAsync(previewFrame);
            PreviewFrameImage.Source = sbSource;
        }
    }
}

private async Task DetectAsync()
{
    IList<DetectedFace> faces = null;
    const BitmapPixelFormat InputPixelFormat = BitmapPixelFormat.Nv12;
    using (VideoFrame destinationPreviewFrame = new VideoFrame(InputPixelFormat, 640, 480))
    {
        await this._mediaCapture.GetPreviewFrameAsync(destinationPreviewFrame);

        if(FaceDetector.IsBitmapPixelFormatSupported(InputPixelFormat))
        {
            faces = await this.DetectFacesAsync(SoftwareBitmap, PreviewFrameImage);

            foreach (var face in faces)
            {
                SoftwareBitmap convertedBitmap = SoftwareBitmap.Convert(destinationPreviewFrame.SoftwareBitmap, BitmapPixelFormat.Rgba16);
                Byte[] rawBytes = await GetBytesFromBitmap(convertedBitmap, BitmapEncoder.BmpEncoderId, face.FaceBox);

                using (Stream stream = rawBytes.AsBuffer().AsStream())
                {
                    var faceAttributesToReturn = new List<FaceAttributeType>()
            {
                FaceAttributeType.Age,
                FaceAttributeType.Emotion,
                FaceAttributeType.Hair
            };

                    Face[] detectedFaces = await this.faceServiceClient.DetectAsync(stream, true, true, faceAttributesToReturn);

                    Debug.Assert(detectedFaces.Length > 0);
                }
            }
        }
    }
}

private async Task<byte[]> GetBytesFromBitmap(SoftwareBitmap soft, Guid encoderId, BitmapBounds bounds)
{
    byte[] array = null;

    using (var ms = new InMemoryRandomAccessStream())
    {
        BitmapEncoder encoder = await BitmapEncoder.CreateAsync(encoderId, ms);
        encoder.SetSoftwareBitmap(soft);

        encoder.BitmapTransform.Bounds = bounds;

        await encoder.FlushAsync();

        array = new byte[ms.Size];

        await ms.ReadAsync(array.AsBuffer(), (uint)ms.Size, InputStreamOptions.None);
    }

    return array;
}

private async Task GetPreviewFrameAsD3DSurfaceAsync()
{ 
    using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync())
    {
        if (currentFrame.Direct3DSurface != null)
        {
            var surface = currentFrame.Direct3DSurface;
            FrameInfoTextBlock.Text = String.Format("{0}x{1} {2}", surface.Description.Width, surface.Description.Height, surface.Description.Format);
        }

        {
            SoftwareBitmap previewFrame = currentFrame.SoftwareBitmap;
            FrameInfoTextBlock.Text = String.Format("{0}x{1} {2}", previewFrame.PixelWidth, previewFrame.PixelHeight, previewFrame.BitmapPixelFormat);
        }

        PreviewFrameImage.Source = null;
    }
}

我不明白错误的来源，DetecFacesAsync是我可以调用Windows.Media.Face.Analysis的方法。对不起我的近似英语。