从MediaCapture访问预览框架

Question

我想抓住我的CaptureElement xaml元素中显示的预览帧.在source我的CaptureElement设置为一个MediaCapture对象,我用的StartPreview()方法开始显示相机.我想访问正在显示的帧而不将它们保存为img或视频文件.目标是从预览中捕获10 fps并将每个帧发送到另一个接受byte []的类.

我尝试使用该CapturePhotoToStorageFileAsync方法,但这不是一个可行的选项,因为我不想拍10张实际图像/秒.我也不想使用ScreenCapture它,因为它存储捕获到视频文件中的内容.理想情况下,我不想暂时将任何媒体文件存储在手机上.看后MSDN的MediaCapture,我注意到有一个名为方法GetPreviewFrameAsync()但是这种方法不的Windows Phone 8.1中存在.我也偶然发现了这个例子,但我并不完全理解它是如何工作的.

任何有关如何处理此问题的建议都非常感谢.

Answer 1

Microsoft github页面上有一个相关的示例,尽管它们的目标是Windows 10.您可能有兴趣迁移项目以获得此功能.

GetPreviewFrame:此示例将捕获预览帧而不是完整的照片.一旦它有预览框架,它就可以编辑它上面的像素.

以下是相关部分:

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;
                }
            }
        }
    }
}

并在课外宣布:

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

当然,您的项目必须允许所有这些的不安全代码才能工作.

仔细查看示例,了解如何获取所有详细信息.或者,要进行演练,您可以观看最近//构建/会议中的摄像机会话,其中包括一些相机示例的演练.