net中捕获摄像头视频的方式及对比

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：

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}）
", 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}）
", 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}）
", 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}）......
", 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}）......
", 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}）
",
                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}）......
", 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}）
",
                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}）
",
                    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;
        }
    }
}