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：
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。
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 image = new Image (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; } }}