如何使用C#创建Windows Webcam应用

原文:如何使用C#创建Windows Webcam应用

最近想用C#写一个camera的应用。搜索了Google和StackOverflow，发现大部分的sample用了WIA或者DirectShow。WIA和DirectShow都没有直接提供C#接口，所以实现起来也比较复杂。试着运行了几个WIA的工程，在Windows10上还不起作用。发现微软提供了一个MediaCapture类，包含了丰富的C#接口，可用于音频，视频。要用这个类，就需要创建一个UWP工程。这里分享下如何使用MediaCapture的C#接口来获取camera的每一帧数据。

微软示例

微软在GitHub上放了大量的UWP示例，里面包含了各种camera的接口使用方法。

在Android中要获取camera的每一帧数据，可以通过onPreviewCallback的回调函数实现。参考CameraFrames这个示例，也可以实现类似的功能。

如何创建Windows Webcam应用

1. 在package.appxmanifest中获取webcam权限：

2. 创建image element用于绘制webcam的预览界面：

3. 通过Image Element初始化FrameRenderer ：

_frameRenderer = new FrameRenderer(PreviewImage);

4. 初始化MediaCapture对象：

// Create a new media capture object.

_mediaCapture = new MediaCapture();

var settings = new MediaCaptureInitializationSettings()

{

    // Select the source we will be reading from.

    SourceGroup = groupModel.SourceGroup,

    // This media capture has exclusive control of the source.

    SharingMode = MediaCaptureSharingMode.ExclusiveControl,

    // Set to CPU to ensure frames always contain CPU SoftwareBitmap images,

    // instead of preferring GPU D3DSurface images.

    MemoryPreference = MediaCaptureMemoryPreference.Cpu,

    // Capture only video. Audio device will not be initialized.

    StreamingCaptureMode = StreamingCaptureMode.Video,

};

try

{

    // Initialize MediaCapture with the specified group.

    // This can raise an exception if the source no longer exists,

    // or if the source could not be initialized.

    await _mediaCapture.InitializeAsync(settings);

    _logger.Log($"Successfully initialized MediaCapture for {groupModel.DisplayName}");

}

catch (Exception exception)

{

    _logger.Log(exception.Message);

    DisposeMediaCapture();

}

5. 使用DeviceWatcher 列出所有设备：

var deviceSelector = MediaFrameSourceGroup.GetDeviceSelector();

_watcher = DeviceInformation.CreateWatcher(deviceSelector);

_watcher.Added += Watcher_Added;

_watcher.Removed += Watcher_Removed;

_watcher.Updated += Watcher_Updated;

_watcher.Start();

private async void Watcher_Added(DeviceWatcher sender, DeviceInformation args)

{

    await AddDeviceAsync(args.Id);

}

private async Task AddDeviceAsync(string id)

{

    var group = await MediaFrameSourceGroup.FromIdAsync(id);

    if (group != null)

    {

        await _dispatcher.RunAsync(CoreDispatcherPriority.Normal, () =>

            {

                _sourceCollection.Add(new FrameSourceGroupModel(group));

            });

    }

}

6. 针对用户的选择更新设备源：

_mediaCapture.FrameSources.TryGetValue(info.SourceInfo.Id, out _source);

7. 通过MediaFrameReader 注册回调函数：

if (_source != null)

{

    _reader = await _mediaCapture.CreateFrameReaderAsync(_source);

    _reader.FrameArrived += Reader_FrameArrived;

}

8. 启动webcam：

MediaFrameReaderStartStatus result = await _reader.StartAsync();

9. 读取并绘制每一帧数据：

private void Reader_FrameArrived(MediaFrameReader sender, MediaFrameArrivedEventArgs args)

{

    // TryAcquireLatestFrame will return the latest frame that has not yet been acquired.

    // This can return null if there is no such frame, or if the reader is not in the

    // "Started" state. The latter can occur if a FrameArrived event was in flight

    // when the reader was stopped.

    using (var frame = sender.TryAcquireLatestFrame())

    {

        _frameRenderer.ProcessFrame(frame);

    }

}

public void ProcessFrame(MediaFrameReference frame)

{

    var softwareBitmap = FrameRenderer.ConvertToDisplayableImage(frame?.VideoMediaFrame);

    if (softwareBitmap != null)

    {

        // Swap the processed frame to _backBuffer and trigger UI thread to render it

        softwareBitmap = Interlocked.Exchange(ref _backBuffer, softwareBitmap);

        // UI thread always reset _backBuffer before using it.  Unused bitmap should be disposed.

        softwareBitmap?.Dispose();

        // Changes to xaml ImageElement must happen in UI thread through Dispatcher

        var task = _imageElement.Dispatcher.RunAsync(CoreDispatcherPriority.Normal,

            async () =>

            {

                // Don't let two copies of this task run at the same time.

                if (_taskRunning)

                {

                    return;

                }

                _taskRunning = true;

                // Keep draining frames from the backbuffer until the backbuffer is empty.

                SoftwareBitmap latestBitmap;

                while ((latestBitmap = Interlocked.Exchange(ref _backBuffer, null)) != null)

                {

                    var imageSource = (SoftwareBitmapSource)_imageElement.Source;

                    await imageSource.SetBitmapAsync(latestBitmap);

                    latestBitmap.Dispose();

                }

                _taskRunning = false;

            });

    }

}

参考

Basic photo, video, and audio capture with MediaCapture

源码

https://github.com/Microsoft/Windows-universal-samples/tree/master/Samples/CameraFrames

巴特西

如何使用C#创建Windows Webcam应用

微软示例

如何创建Windows Webcam应用

参考

源码

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