c#-WinRT从视频流中提取帧

我使用内置摄像头解码条形码,我使用capElement.Source.CapturePhotoToStreamAsync来从预览中捕获照片.它可以正常工作,但是暂时冻结了该应用程序,感觉非常笨拙且有故障.

因此,我希望在后台进行此操作,同时至少在处理照片时保留响应式UI.

到目前为止,我想出了这个来捕获视频流：

 private async void ScanInBackground()
        {
            bool failedScan = true;

            var stream = new InMemoryRandomAccessStream();

            await  capElement.Source.StartRecordToStreamAsync(MediaEncodingProfile.CreateWmv(VideoEncodingQuality.HD1080p), stream);

            while(failedScan)
            {
                Byte[] bytes = await GetBytesFromStream(stream);
                //How to split the bytes into frames?

                Task.Delay(50);
            }

            Dispatcher.RunAsync(CoreDispatcherPriority.Low,() => StopCap()); 
        }

以及从流中获取字节的方法：

public static async Task<byte[]> GetBytesFromStream(IRandomAccessStream randomStream)
        {
            var reader = new DataReader(randomStream.GetInputStreamAt(0));
            var bytes = new byte[randomStream.Size];
            try
            {
                await reader.LoadAsync((uint)randomStream.Size); reader.ReadBytes(bytes);
            }
            catch(Exception ex)
            {
                Logger.LogExceptionAsync(ex, "GetBytesFromStream");
            }
            return bytes;
        }

从ScanInBackground上的评论中,您可以看到我不知道如何将流分割成照片/帧.

解决方法:

尽管它们是针对Windows 10的,但在Microsoft github页面上有一个相关的示例.您可能有兴趣迁移项目以获取此功能.

GetPreviewFrame：此示例将捕获预览框架,而不是完整的照片.具有预览框后,便可以读取和编辑其上的像素.

这是相关的部分：

private async Task GetPreviewFrameAsSoftwareBitmapAsync()
{
    // Get information about the preview
    var previewProperties = _mediaCapture.VideoDeviceController.GetMediaStreamProperties(MediaStreamType.VideoPreview) as VideoEncodingProperties;

    // Create the video frame to request a SoftwareBitmap preview frame
    var videoFrame = new VideoFrame(BitmapPixelFormat.Bgra8, (int)previewProperties.Width, (int)previewProperties.Height);

    // Capture the preview frame
    using (var currentFrame = await _mediaCapture.GetPreviewFrameAsync(videoFrame))
    {
        // Collect the resulting frame
        SoftwareBitmap previewFrame = currentFrame.SoftwareBitmap;

        // Add a simple green filter effect to the SoftwareBitmap
        EditPixels(previewFrame);
    }
}

private unsafe void EditPixels(SoftwareBitmap bitmap)
{
    // Effect is hard-coded to operate on BGRA8 format only
    if (bitmap.BitmapPixelFormat == BitmapPixelFormat.Bgra8)
    {
        // In BGRA8 format, each pixel is defined by 4 bytes
        const int BYTES_PER_PIXEL = 4;

        using (var buffer = bitmap.LockBuffer(BitmapBufferAccessMode.ReadWrite))
        using (var reference = buffer.CreateReference())
        {
            // Get a pointer to the pixel buffer
            byte* data;
            uint capacity;
            ((IMemoryBufferByteAccess)reference).GetBuffer(out data, out capacity);

            // Get information about the BitmapBuffer
            var desc = buffer.GetPlaneDescription(0);

            // Iterate over all pixels
            for (uint row = 0; row < desc.Height; row++)
            {
                for (uint col = 0; col < desc.Width; col++)
                {
                    // Index of the current pixel in the buffer (defined by the next 4 bytes, BGRA8)
                    var currPixel = desc.StartIndex + desc.Stride * row + BYTES_PER_PIXEL * col;

                    // Read the current pixel information into b,g,r channels (leave out alpha channel)
                    var b = data[currPixel + 0]; // Blue
                    var g = data[currPixel + 1]; // Green
                    var r = data[currPixel + 2]; // Red

                    // Boost the green channel, leave the other two untouched
                    data[currPixel + 0] = b;
                    data[currPixel + 1] = (byte)Math.Min(g + 80, 255);
                    data[currPixel + 2] = r;
                }
            }
        }
    }
}

并在您的课外声明：

[ComImport]
[Guid("5b0d3235-4dba-4d44-865e-8f1d0e4fd04d")]
[InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
unsafe interface IMemoryBufferByteAccess
{
    void GetBuffer(out byte* buffer, out uint capacity);
}

当然,您的项目必须允许不安全的代码才能使所有这些工作.

仔细查看示例以了解如何获取所有详细信息.或者,要进行演练,您可以从最近的// build /会议中观看camera session,其中包括一些摄像机样本的演练.

标签：windows-runtime,windows-8-1,c
来源： https://codeday.me/bug/20191120/2040334.html