MediaCapture.StartPreviewToCustomSinkAsync 方法如何工作？

Question

为什么 Windows 文档如此缺乏？？似乎无法找到此方法应该如何工作的示例 StartPreviewToCustomSinkAsync

我想做的是从视频源获取预览图像（通过 MediaCapture) but can't understand how this method works (especially what the second parameter, IMediaExtension，应该是 be/do）。

你们有没有机会帮我解决这个问题？

Answer 1

GitHub. If you are developing for Windows Phone 8.1 - samples are here
上有很多例子根据 this 示例记录如下所示：

private StspMediaSinkProxy mediaSink;
mediaSink = new StspMediaSinkProxy();

MediaEncodingProfile encodingProfile = MediaEncodingProfile.CreateMp4(VideoEncodingQuality.Qvga);

var mfExtension = await mediaSink.InitializeAsync(encodingProfile.Audio, encodingProfile.Video);
await mediaCapture.StartRecordToCustomSinkAsync(encodingProfile, mfExtension);

所以，您可以从这个例子中了解如何从 MediaEncodingProfile 中获取 IMediaExtension。
您没有 post 任何代码，但制作预览应该类似于我提供的代码

Answer 2

如果您只需要时不时地获取预览帧，Microsoft github 页面上有一个相关的示例，尽管它们的目标是 Windows 10。您可能有兴趣迁移您的项目以获得此功能。

GetPreviewFrame：此示例将捕获预览帧而不是 full-blown 照片。一旦有了预览框，就可以编辑其中的像素。

相关部分如下：

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 class 之外声明：

[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正常工作。

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 //build/ 会议的 camera session，其中包括一些相机示例的演练。

或者，如果你绑定到 8.1，你可以查看 Lumia Imaging SDK, which can notify you when there's a new preview frame available.

MediaCapture.StartPreviewToCustomSinkAsync 方法如何工作？

How does MediaCapture.StartPreviewToCustomSinkAsync method work?

.net

c#

windows-runtime

windows-phone-8.1