.net中捕获摄像头视频的方式及对比(How to Capture Camera Video via .Net)

前言     随着Windows操作系统的不断演变，用于捕获视频的API接口也在进化，微软提供了VFW、DirectShow和MediaFoundation这三代接口。其中VFW早已被DirectShow取代，而最新的MediaFoundation被Windows Vista和Windows 7所支持。可惜的是，上述接口基于COM技术且灵活性很大，在.net中并不方便直接使用。 .net封装     老外有很多活雷锋，他们奉献了不少的开源项目，DirectShow.net是对DirectShow的封装，而MediaFoundation.net是对MediaFoundation的封装。它们都能在 http://sourceforge.net上找到。这两个封装之后的类库基本上跟原来的COM是一一对应的关系，可以用于视频捕获，但是用起来还是不够简便。     通过不断的google搜索，我认为以下类库对视频捕获封装得不错，它们是：DirectX.Capture、OpenCv、EmguCv和AForge。 DirectX.Capture     DirectX.Capture是发表在CodeProject上的一个项目，它能很方便的捕获视频和音频，在窗口预览，并将结果保存到文件。使用DirectX.Capture的示例如下：

DirectX.Capture

Capture capture = new Capture( Filters.VideoInputDevices[ 0 ], Filters.AudioInputDevices[ 1 ] ); capture.Filename = " C:\MyVideo.avi " ; capture.Start(); // ... capture.Stop();

但是，它没有提供单独获取某帧内容的方法。如果您只是需要预览并保存视频，它很好用。
OpenCv
    OpenCv对VFW和DirectShow的视频捕获部分进行了很好的封装，能够很方便的获取到某帧的内容，也可以将结果保存到视频文件中。使用OpenCv的示例如下：

OpenCv

IntPtr ptrCapture = CvInvoke.cvCreateCameraCapture(param.deviceInfo.Index); while ( ! stop) { IntPtr ptrImage = CvInvoke.cvQueryFrame(ptrCapture); lock (lockObject) { stop = stopCapture; } } CvInvoke.cvReleaseCapture( ref ptrCapture);

      不过OpenCv并未对音频捕获进行封装，如果需要同时录制音频，这个搞不定。
值得注意的是，从OpenCv 1.1开始已经实现了对DirectShow的封装，这跟网上很多人所说的OpenCv使用VFW进行视频捕获效率低下这种观点不一致。关于OpenCv使用DirectShow的论据请看本文的附录。
EmguCv
    EmguCv是对OpenCv在.net的封装，继承了OpenCv快速的优点，同时它更加好用。使用EmguCv的示例代码如下：

EmguCv

Capture capture = new Capture(param.deviceInfo.Index); while ( ! stop) { pbCapture.Image = capture.QueryFrame().Bitmap; lock (lockObject) { stop = stopCapture; } } capture.Dispose();

 

 

AForge
    AForge是一套纯正的.net开源图像处理类库，它的视频捕获类也是基于DirectShow的，但更加好用，功能更多，从使用和帮助来看更类似微软的类库。

AForge

captureAForge = new VideoCaptureDevice(cameraDevice.MonikerString); captureAForge.NewFrame += new NewFrameEventHandler(captureAForge_NewFrame); captureAForge.Start(); // ... captureAForge.SignalToStop(); private void captureAForge_NewFrame( object sender, NewFrameEventArgs eventArgs) { pbCapture.Image = (Bitmap)eventArgs.Frame.Clone(); }

 

对比
    介绍完它们之后，我们来比较下它们。它们都是基于DirectShow的，所以性能几乎一样。实际上，我个人认为，摄像头所用的硬件和驱动程序的支持对性能影响更大。我的摄像头在Windows 7下没有专门的驱动程序，只能使用Microsoft提供的默认驱动，性能比WindowsXp要差一截。
值得注意的是主要有几点：
    （1）只有DirectX.Capture实现了对音频的捕获；
    （2）只有DirectX.Capture不能获取单独的某帧图像；
    （3）EmguCv的免费版基于商业许可，而其他类库的许可都很宽松；
    （4）AForge的示例和帮助比较好，而且功能多些。

 

附录：OpenCv也用DirectShow来捕获视频
通过分析OpenCv 2.0的源代码，我得出了OpenCv使用DirectShow来捕获视频的结论。证据如下：

DirectShow In OpenCv

（ 1 ） // _highgui.h line:100 #if (_MSC_VER >= 1400 || defined __GNUC__) && !defined WIN64 && !defined _WIN64 #define HAVE_VIDEOINPUT 1 #endif （ 2 ） // cvcap_dshow.cpp line:44 #ifdef HAVE_VIDEOINPUT #include " videoinput.h " /* ******************** Capturing video from camera via VFW ******************** */ class CvCaptureCAM_DShow : public CvCapture （ 3 ） // cvapp.cpp line:102 CV_IMPL CvCapture * cvCreateCameraCapture ( int index) { // ..... // line:140 switch (domains[i]) { #ifdef HAVE_VIDEOINPUT case CV_CAP_DSHOW: capture = cvCreateCameraCapture_DShow (index); if (capture) return capture; break ; #endif

 

本文完整源代码

完整代码

using System; using System.Collections.Generic; using System.ComponentModel; using System.Data; using System.Drawing; using System.Linq; using System.Text; using System.Windows.Forms; using System.Diagnostics; using System.Runtime.InteropServices; using AForge.Video; using AForge.Video.DirectShow; using Emgu.CV; using Emgu.CV.CvEnum; using Emgu.CV.Structure; using Emgu.CV.UI; using System.Threading; namespace ImageProcessLearn { public partial class FormCameraCapture : Form { private int framesCaptured; // 已经捕获的视频帧数 private int frameCount; // 需要捕获的总帧数 private Stopwatch sw; // 计时器 private VideoCaptureDevice captureAForge = null ; // AForge视频捕获对象 private bool stopCapture; // 是否停止捕获视频 private object lockObject = new object (); public FormCameraCapture() { InitializeComponent(); sw = new Stopwatch(); } // 窗体加载时，获取视频捕获设备列表 private void FormCameraCapture_Load( object sender, EventArgs e) { FilterInfoCollection videoDevices = new FilterInfoCollection(FilterCategory.VideoInputDevice); if (videoDevices != null && videoDevices.Count > 0 ) { int idx = 0 ; foreach (FilterInfo device in videoDevices) { cmbCaptureDevice.Items.Add( new DeviceInfo(device.Name, device.MonikerString, idx, FilterCategory.VideoInputDevice)); idx ++ ; } cmbCaptureDevice.SelectedIndex = 0 ; } } // 当改变视频设备时，重新填充该设备对应的能力 private void cmbCaptureDevice_SelectedIndexChanged( object sender, EventArgs e) { if (cmbCaptureDevice.SelectedItem != null ) { // 保存原来选择的设备能力 Size oldFrameSize = new Size( 0 , 0 ); int oldMaxFrameRate = 0 ; if (cmbDeviceCapability.SelectedItem != null ) { oldFrameSize = ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize; oldMaxFrameRate = ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).MaxFrameRate; } // 清除设备能力 cmbDeviceCapability.Items.Clear(); // 添加新的设备能力 int oldCapIndex = - 1 ; // 原来选择的设备能力的新索引 VideoCaptureDevice video = new VideoCaptureDevice(((DeviceInfo)cmbCaptureDevice.SelectedItem).MonikerString); for ( int i = 0 ; i < video.VideoCapabilities.Length; i ++ ) { VideoCapabilities cap = video.VideoCapabilities[i]; DeviceCapabilityInfo capInfo = new DeviceCapabilityInfo(cap.FrameSize, cap.MaxFrameRate); cmbDeviceCapability.Items.Add(capInfo); if (oldFrameSize == capInfo.FrameSize && oldMaxFrameRate == capInfo.MaxFrameRate) oldCapIndex = i; } // 重新选择原来的设备能力，或者选一个新的能力 if (oldCapIndex == - 1 ) oldCapIndex = 0 ; cmbDeviceCapability.SelectedIndex = oldCapIndex; } } // 当改变设备能力时 private void cmbDeviceCapability_SelectedIndexChanged( object sender, EventArgs e) { if ( int .Parse(txtRate.Text) >= ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).MaxFrameRate) txtRate.Text = ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).MaxFrameRate.ToString(); } // 性能测试：测试获取指定帧数的视频，并将其转换成图像，所需要的时间，然后计算出FPS private void btnPerformTest_Click( object sender, EventArgs e) { int frameCount = int .Parse(txtFrameCount.Text); if (frameCount <= 0 ) frameCount = 300 ; DeviceInfo device = (DeviceInfo)cmbCaptureDevice.SelectedItem; btnPerformTest.Enabled = false ; btnStart.Enabled = false ; txtResult.Text += PerformTestWithAForge(device.MonikerString, frameCount); txtResult.Text += PerformTestWithEmguCv(device.Index, frameCount); txtResult.Text += PerformTestWithOpenCv(device.Index, frameCount); btnPerformTest.Enabled = true ; btnStart.Enabled = true ; } // AForge性能测试 private string PerformTestWithAForge( string deviceMonikerString, int frameCount) { VideoCaptureDevice video = new VideoCaptureDevice(deviceMonikerString); video.NewFrame += new NewFrameEventHandler(PerformTest_NewFrame); video.DesiredFrameSize = ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize; video.DesiredFrameRate = int .Parse(txtRate.Text); framesCaptured = 0 ; this .frameCount = frameCount; video.Start(); sw.Reset(); sw.Start(); video.WaitForStop(); double time = sw.Elapsed.TotalMilliseconds; return string .Format( " AForge性能测试，帧数：{0}，耗时：{1:F05}毫秒，FPS:{2:F02}，设定（{3}）\r\n " , frameCount, time, 1000d * frameCount / time, GetSettings()); } void PerformTest_NewFrame( object sender, NewFrameEventArgs eventArgs) { framesCaptured ++ ; if (framesCaptured > frameCount) { sw.Stop(); VideoCaptureDevice video = sender as VideoCaptureDevice; video.SignalToStop(); } } // EmguCv性能测试 private string PerformTestWithEmguCv( int deviceIndex, int frameCount) { Capture video = new Capture(deviceIndex); video.SetCaptureProperty(CAP_PROP.CV_CAP_PROP_FRAME_WIDTH, ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize.Width); video.SetCaptureProperty(CAP_PROP.CV_CAP_PROP_FRAME_HEIGHT, ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize.Height); video.SetCaptureProperty(CAP_PROP.CV_CAP_PROP_FPS, double .Parse(txtRate.Text)); sw.Reset(); sw.Start(); for ( int i = 0 ; i < frameCount; i ++ ) video.QueryFrame(); sw.Stop(); video.Dispose(); double time = sw.Elapsed.TotalMilliseconds; return string .Format( " EmguCv性能测试，帧数：{0}，耗时：{1:F05}毫秒，FPS:{2:F02}，设定（{3}）\r\n " , frameCount, time, 1000d * frameCount / time, GetSettings()); } // OpenCv性能测试 private string PerformTestWithOpenCv( int deviceIndex, int frameCount) { IntPtr ptrVideo = CvInvoke.cvCreateCameraCapture(deviceIndex); CvInvoke.cvSetCaptureProperty(ptrVideo, CAP_PROP.CV_CAP_PROP_FRAME_WIDTH, ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize.Width); CvInvoke.cvSetCaptureProperty(ptrVideo, CAP_PROP.CV_CAP_PROP_FRAME_HEIGHT, ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize.Height); CvInvoke.cvSetCaptureProperty(ptrVideo, CAP_PROP.CV_CAP_PROP_FPS, double .Parse(txtRate.Text)); sw.Reset(); sw.Start(); for ( int i = 0 ; i < frameCount; i ++ ) CvInvoke.cvQueryFrame(ptrVideo); sw.Stop(); CvInvoke.cvReleaseCapture( ref ptrVideo); double time = sw.Elapsed.TotalMilliseconds; return string .Format( " OpenCv性能测试，帧数：{0}，耗时：{1:F05}毫秒，FPS:{2:F02}，设定（{3}）\r\n " , frameCount, time, 1000d * frameCount / time, GetSettings()); } // 得到设置所对应的字符串 private string GetSettings() { return string .Format( " 摄像头：{0}，尺寸：{1}x{2}，FPS：{3} " , ((DeviceInfo)cmbCaptureDevice.SelectedItem).Name, ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize.Width, ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize.Height, txtRate.Text); } // 开始捕获视频 private void btnStart_Click( object sender, EventArgs e) { // 得到设置项 DeviceInfo cameraDevice = (DeviceInfo)cmbCaptureDevice.SelectedItem; Size frameSize = ((DeviceCapabilityInfo)cmbDeviceCapability.SelectedItem).FrameSize; int rate = int .Parse(txtRate.Text); ThreadParam param = new ThreadParam(cameraDevice, new DeviceCapabilityInfo(frameSize, rate)); if (rbAForge.Checked) { captureAForge = new VideoCaptureDevice(cameraDevice.MonikerString); captureAForge.DesiredFrameSize = frameSize; captureAForge.DesiredFrameRate = rate; captureAForge.NewFrame += new NewFrameEventHandler(captureAForge_NewFrame); txtResult.Text += string .Format( " 开始捕获视频（方式：AForge，开始时间：{0}）......\r\n " , DateTime.Now.ToLongTimeString()); framesCaptured = 0 ; sw.Reset(); sw.Start(); captureAForge.Start(); } else if (rbEmguCv.Checked) { stopCapture = false ; Thread captureThread = new Thread( new ParameterizedThreadStart(CaptureWithEmguCv)); captureThread.Start(param); } else if (rbOpenCv.Checked) { stopCapture = false ; Thread captureThread = new Thread( new ParameterizedThreadStart(CaptureWithOpenCv)); captureThread.Start(param); } btnStart.Enabled = false ; btnStop.Enabled = true ; btnPerformTest.Enabled = false ; } private void captureAForge_NewFrame( object sender, NewFrameEventArgs eventArgs) { pbCapture.Image = (Bitmap)eventArgs.Frame.Clone(); lock (lockObject) { framesCaptured ++ ; } } // EmguCv视频捕获 private void CaptureWithEmguCv( object objParam) { bool stop = false ; int framesCaptured = 0 ; Stopwatch sw = new Stopwatch(); txtResult.Invoke( new AddResultDelegate(AddResultMethod), string .Format( " 开始捕获视频（方式：EmguCv，开始时间：{0}）......\r\n " , DateTime.Now.ToLongTimeString())); ThreadParam param = (ThreadParam)objParam; Capture capture = new Capture(param.deviceInfo.Index); capture.SetCaptureProperty(CAP_PROP.CV_CAP_PROP_FRAME_WIDTH, param.deviceCapability.FrameSize.Width); capture.SetCaptureProperty(CAP_PROP.CV_CAP_PROP_FRAME_HEIGHT, param.deviceCapability.FrameSize.Height); capture.SetCaptureProperty(CAP_PROP.CV_CAP_PROP_FPS, param.deviceCapability.MaxFrameRate); sw.Start(); while ( ! stop) { pbCapture.Image = capture.QueryFrame().Bitmap; framesCaptured ++ ; lock (lockObject) { stop = stopCapture; } } sw.Stop(); txtResult.Invoke( new AddResultDelegate(AddResultMethod), string .Format( " 捕获视频结束（方式：EmguCv，结束时间：{0}，用时：{1:F05}毫秒，帧数：{2}，FPS：{3:F02}）\r\n " , DateTime.Now.ToLongTimeString(), sw.Elapsed.TotalMilliseconds, framesCaptured, framesCaptured / sw.Elapsed.TotalSeconds)); capture.Dispose(); } // OpenCv视频捕获 private void CaptureWithOpenCv( object objParam) { bool stop = false ; int framesCaptured = 0 ; Stopwatch sw = new Stopwatch(); txtResult.Invoke( new AddResultDelegate(AddResultMethod), string .Format( " 开始捕获视频（方式：OpenCv，开始时间：{0}）......\r\n " , DateTime.Now.ToLongTimeString())); ThreadParam param = (ThreadParam)objParam; IntPtr ptrCapture = CvInvoke.cvCreateCameraCapture(param.deviceInfo.Index); CvInvoke.cvSetCaptureProperty(ptrCapture, CAP_PROP.CV_CAP_PROP_FRAME_WIDTH, param.deviceCapability.FrameSize.Width); CvInvoke.cvSetCaptureProperty(ptrCapture, CAP_PROP.CV_CAP_PROP_FRAME_HEIGHT, param.deviceCapability.FrameSize.Height); CvInvoke.cvSetCaptureProperty(ptrCapture, CAP_PROP.CV_CAP_PROP_FPS, param.deviceCapability.MaxFrameRate); sw.Start(); while ( ! stop) { IntPtr ptrImage = CvInvoke.cvQueryFrame(ptrCapture); MIplImage iplImage = (MIplImage)Marshal.PtrToStructure(ptrImage, typeof (MIplImage)); Image < Bgr, byte > image = new Image < Bgr, byte > (iplImage.width, iplImage.height, iplImage.widthStep, iplImage.imageData); pbCapture.Image = image.Bitmap; // pbCapture.Image = ImageConverter.IplImagePointerToBitmap(ptrImage); framesCaptured ++ ; lock (lockObject) { stop = stopCapture; } } sw.Stop(); txtResult.Invoke( new AddResultDelegate(AddResultMethod), string .Format( " 捕获视频结束（方式：OpenCv，结束时间：{0}，用时：{1:F05}毫秒，帧数：{2}，FPS：{3:F02}）\r\n " , DateTime.Now.ToLongTimeString(), sw.Elapsed.TotalMilliseconds, framesCaptured, framesCaptured / sw.Elapsed.TotalSeconds)); CvInvoke.cvReleaseCapture( ref ptrCapture); } // 停止捕获视频 private void btnStop_Click( object sender, EventArgs e) { if (captureAForge != null ) { sw.Stop(); if (captureAForge.IsRunning) captureAForge.SignalToStop(); captureAForge = null ; txtResult.Text += string .Format( " 捕获视频结束（方式：AForge，结束时间：{0}，用时：{1:F05}毫秒，帧数：{2}，FPS：{3:F02}）\r\n " , DateTime.Now.ToLongTimeString(), sw.Elapsed.TotalMilliseconds, framesCaptured, framesCaptured / sw.Elapsed.TotalSeconds); } lock (lockObject) { stopCapture = true ; } btnStart.Enabled = true ; btnStop.Enabled = false ; btnPerformTest.Enabled = true ; } // 用于在工作线程中更新结果的委托及方法 public delegate void AddResultDelegate( string result); public void AddResultMethod( string result) { txtResult.Text += result; } } // 设备信息 public struct DeviceInfo { public string Name; public string MonikerString; public int Index; Guid Category; public DeviceInfo( string name, string monikerString, int index) : this (name, monikerString, index, Guid.Empty) { } public DeviceInfo( string name, string monikerString, int index, Guid category) { Name = name; MonikerString = monikerString; Index = index; Category = category; } public override string ToString() { return Name; } } // 设备能力 public struct DeviceCapabilityInfo { public Size FrameSize; public int MaxFrameRate; public DeviceCapabilityInfo(Size frameSize, int maxFrameRate) { FrameSize = frameSize; MaxFrameRate = maxFrameRate; } public override string ToString() { return string .Format( " {0}x{1} {2}fps " , FrameSize.Width, FrameSize.Height, MaxFrameRate); } } // 传递到捕获视频工作线程的参数 public struct ThreadParam { public DeviceInfo deviceInfo; public DeviceCapabilityInfo deviceCapability; public ThreadParam(DeviceInfo deviceInfo, DeviceCapabilityInfo deviceCapability) { this .deviceInfo = deviceInfo; this .deviceCapability = deviceCapability; } } }