关于 web cam 使用自家的摄像头实现视频捕捉技术高级篇

网络上一大堆的视频捕捉代码，比如：

代码

public class WebCameraEngine
    {
        //  showVideo  calls
        [DllImport("avicap32.dll")]
        public static extern IntPtr capCreateCaptureWindowA(byte[] lpszWindowName, int dwStyle, int x, int y, int nWidth, int nHeight, IntPtr hWndParent, int nID);
        [DllImport("avicap32.dll")]
        public static extern bool capGetDriverDescriptionA(short wDriver, byte[] lpszName, int cbName, byte[] lpszVer, int cbVer);
        [DllImport("User32.dll")]
        public static extern bool SendMessage(IntPtr hWnd, int wMsg, bool wParam, int lParam);
        [DllImport("User32.dll")]
        public static extern bool SendMessage(IntPtr hWnd, int wMsg, short wParam, int lParam);
        [DllImport("User32.dll")]
        public static extern bool SendMessage(IntPtr hWnd, int wMsg, short wParam, FrameEventHandler lParam);
        [DllImport("User32.dll")]
        public static extern bool SendMessage(IntPtr hWnd, int wMsg, int wParam, ref BitMapInfo lParam);
        [DllImport("User32.dll")]
        public static extern int SetWindowPos(IntPtr hWnd, int hWndInsertAfter, int x, int y, int cx, int cy, int wFlags);
        [DllImport("avicap32.dll")]
        public static extern int capGetVideoFormat(IntPtr hWnd, IntPtr psVideoFormat, int wSize);

        //  constants
        public const int WM_USER = 0x400;

        public const int WS_CHILD = 0x40000000;
        public const int WS_VISIBLE = 0x10000000;

        public const int WM_CAP_DRIVER_CONNECT = WM_USER + 10;
        public const int WM_CAP_DRIVER_DISCONNECT = WM_USER + 11;

        public const int WM_CAP_START = WM_USER;
        public const int WM_CAP_STOP = WM_CAP_START + 68;

        public const int WM_CAP_SAVEDIB = WM_CAP_START + 25;
        public const int WM_CAP_GRAB_FRAME = WM_CAP_START + 60;
        public const int WM_CAP_FILE_SET_CAPTURE_FILEA = WM_CAP_START + 20;
        public const int WM_CAP_SEQUENCE = WM_CAP_START + 62;
        public const int WM_CAP_SEQUENCE_NOFILE = WM_CAP_START + 63;

        public const int WM_CAP_SET_OVERLAY = WM_CAP_START + 51;
        public const int WM_CAP_SET_CALLBACK_FRAME = WM_USER + 5;
        public const int WM_CAP_SET_PREVIEW = WM_USER + 50;
        public const int WM_CAP_SET_PREVIEWRATE = WM_USER + 52;
        public const int WM_CAP_SET_CALLBACK_VIDEOSTREAM = WM_CAP_START + 6;
        public const int WM_CAP_SET_CALLBACK_ERROR = WM_CAP_START + 2;
        public const int WM_CAP_SET_CALLBACK_STATUSA = WM_CAP_START + 3;
        public const int WM_CAP_SET_SCALE = WM_CAP_START + 53;
        public const int WM_CAP_SET_VIDEOFORMAT = WM_USER + 45;

        public const int SWP_NOMOVE = 0x2;
        public const int SWP_NOZORDER = 0x4;

        //  Structures
        [StructLayout(LayoutKind.Sequential)]
        public struct VideoHdr
        {
            [MarshalAs(UnmanagedType.I4)]
            public int lpData;
            [MarshalAs(UnmanagedType.I4)]
            public int dwBufferLength;
            [MarshalAs(UnmanagedType.I4)]
            public int dwBytesUsed;
            [MarshalAs(UnmanagedType.I4)]
            public int dwTimeCaptured;
            [MarshalAs(UnmanagedType.I4)]
            public int dwUser;
            [MarshalAs(UnmanagedType.I4)]
            public int dwFlags;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 4)]
            public int[] dwReserved;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct BitMapInfoHeader
        {
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biSize;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biWidth;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biHeight;
            [MarshalAs(UnmanagedType.I2)]
            public short biPlanes;
            [MarshalAs(UnmanagedType.I2)]
            public short biBitCount;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biCompression;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biSizeImage;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biXPelsPerMeter;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biYPelsPerMeter;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biClrUsed;
            [MarshalAs(UnmanagedType.I4)]
            public Int32 biClrImportant;
        }

        [StructLayout(LayoutKind.Sequential)]
        public struct BitMapInfo
        {
            [MarshalAs(UnmanagedType.Struct, SizeConst = 40)]
            public BitMapInfoHeader bmiHeader;
            [MarshalAs(UnmanagedType.ByValArray, SizeConst = 1024)]
            public Int32[] bmiColors;
        }

        public delegate void FrameEventHandler(IntPtr lwnd, IntPtr lpVHdr);

        //  Public  methods
        public static object GetStructure(IntPtr ptr, ValueType structure)
        {
            return Marshal.PtrToStructure(ptr, structure.GetType());
        }

        public static object GetStructure(int ptr, ValueType structure)
        {
            return GetStructure(new IntPtr(ptr), structure);
        }

        public static void Copy(IntPtr ptr, byte[] data)
        {
            Marshal.Copy(ptr, data, 0, data.Length);
        }

        public static void Copy(int ptr, byte[] data)
        {
            Copy(new IntPtr(ptr), data);
        }

        public static int SizeOf(object structure)
        {
            return Marshal.SizeOf(structure);
        }
    }

但是使用的例子却没有，特别关于视频流的问题。因此我特地查看了msdn。现在把研究过程写下来：

http://msdn.microsoft.com/en-us/library/ms713477(VS.85).aspx

在c#里面的例子，实际上使用了AVICap这个c++的类库。他的功能包括：

1. 捕捉视频音频到avi文件

2. 动态链接、断开捕捉设备

3. 查看实时的视频信号

4. 设置捕捉率

5. 显示设置对话框、palettes

6. 拷贝图像到剪贴板

7. 对单个图像进行截图+保存为DIB

8. Specify a file to use when capturing and copy the contents of the capture file to another file.（这个没太理解）

现在对avicap所有方法进行说明：

1. 建立一个捕捉窗口：

代码

hWndC = capCreateCaptureWindow (
    (LPSTR) "My Capture Window", // window name if pop-up
    WS_CHILD | WS_VISIBLE,       // window style
    0, 0, 160, 120,              // window position and dimensions
    (HWND) hwndParent,
    (int) nID /* child ID *

2. 链接捕捉设备

代码

fOK = SendMessage (hWndC, WM_CAP_DRIVER_CONNECT, 0, 0L);
//
// Or, use the macro to connect to the MSVIDEO driver:
// fOK = capDriverConnect(hWndC, 0);
//
// Place code to set up and capture video here.
//
capDriverDisconnect (hWndC);

3. 枚举可以使用的捕捉设备：

char szDeviceName[80];
char szDeviceVersion[80];

for (wIndex = 0; wIndex < 10; wIndex++)
{
    if (capGetDriverDescription(
            wIndex,
            szDeviceName,
            sizeof (szDeviceName),
            szDeviceVersion,
            sizeof (szDeviceVersion)
        ))
    {
        // Append name to list of installed capture drivers
        // and then let the user select a driver to use.
    }
}

4. 获取捕捉设备的能力

代码

CAPDRIVERCAPS CapDrvCaps;

SendMessage (hWndC, WM_CAP_DRIVER_GET_CAPS,
sizeof (CAPDRIVERCAPS), (LONG) (LPVOID) &CapDrvCaps);

// Or, use the macro to retrieve the driver capabilities.
// capDriverGetCaps(hWndC, &CapDrvCaps, sizeof (CAPDRIVERCAPS));

5. 获取捕捉窗口的状态

CAPSTATUS CapStatus;

capGetStatus(hWndC, &CapStatus, sizeof (CAPSTATUS));

SetWindowPos(hWndC, NULL, 0, 0, CapStatus.uiImageWidth,
CapStatus.uiImageHeight, SWP_NOZORDER | SWP_NOMOVE)

6. 显示设置捕捉窗口

代码

CAPDRIVERCAPS CapDrvCaps;

capDriverGetCaps(hWndC, &CapDrvCaps, sizeof (CAPDRIVERCAPS));

// Video source dialog box.
if (CapDriverCaps.fHasDlgVideoSource)
    capDlgVideoSource(hWndC);

// Video format dialog box.
if (CapDriverCaps.fHasDlgVideoFormat)
{
    capDlgVideoFormat(hWndC);

    // Are there new image dimensions?
    capGetStatus(hWndC, &CapStatus, sizeof (CAPSTATUS));

    // If so, notify the parent of a size change.
}

// Video display dialog box.
if (CapDriverCaps.fHasDlgVideoDisplay)
    capDlgVideoDisplay(hWndC);

7. 预览图像

capPreviewRate(hWndC, 66);     // rate, in milliseconds
capPreview(hWndC, TRUE);       // starts preview

// Preview

capPreview(hWnd, FALSE);        // disables preview

8. 判断是否允许图像叠加（overlay）

CAPDRIVERCAPS CapDrvCaps;

capDriverGetCaps(hWndC, &CapDrvCaps, sizeof (CAPDRIVERCAPS));

if (CapDrvCaps.fHasOverlay)
capOverlay(hWndC, TRUE);

9. 对视频捕捉文件命名

char szCaptureFile[] = "MYCAP.AVI";

capFileSetCaptureFile( hWndC, szCaptureFile);
capFileAlloc( hWndC, (1024L * 1024L * 5));

10. 设置声音捕捉

代码

WAVEFORMATEX wfex;

wfex.wFormatTag = WAVE_FORMAT_PCM;
wfex.nChannels = 2; // Use stereo
wfex.nSamplesPerSec = 11025;
wfex.nAvgBytesPerSec = 22050;
wfex.nBlockAlign = 2;
wfex.wBitsPerSample = 8;
wfex.cbSize = 0;

capSetAudioFormat(hWndC, &wfex, sizeof(WAVEFORMATEX));

11. 改变视频捕捉设置

代码

CAPTUREPARMS CaptureParms;
float FramesPerSec = 10.0;

capCaptureGetSetup(hWndC, &CaptureParms, sizeof(CAPTUREPARMS));

CaptureParms.dwRequestMicroSecPerFrame = (DWORD) (1.0e6 /
FramesPerSec);
capCaptureSetSetup(hWndC, &CaptureParms, sizeof (CAPTUREPARMS));

12. 捕捉数据并保存

char szNewName[] = "NEWFILE.AVI";

// Set up the capture operation.

capCaptureSequence(hWndC);

// Capture.

capFileSaveAs(hWndC, szNewName);

13. 在视频文件中叠加信息

代码

// This example assumes the application controls
// the video source for preroll and postroll.
CAPINFOCHUNK cic;
// .
// .
// .
cic.fccInfoID = infotypeSMPTE_TIME;
cic.lpData = "00:20:30:12";
cic.cbData = strlen (cic.lpData) + 1;
capFileSetInfoChunk (hwndC, &cic);

14. 添加一个帧回调函数

代码

TCHAR gachBuffer[100];  // Global buffer.

DWORD gdwFrameNum = 0;

// FrameCallbackProc: frame callback function.

// hWnd:              capture window handle.

// lpVHdr:            pointer to structure containing captured

//                        frame information.

//

LRESULT PASCAL FrameCallbackProc(HWND hWnd, LPVIDEOHDR lpVHdr)

{

    if (!hWnd)

        return FALSE;

    _stprintf_s(gachBuffer, TEXT("Preview frame# %ld "), gdwFrameNum++);

    SetWindowText(hWnd, gachBuffer);

    return (LRESULT) TRUE ;

}

15. Adding Callback Functions to an Application

16. Creating a Status Callback Function

17. Creating an Error Callback Function

reference

基本上可以看到，网上那个非常简单的c#封装实际上还有很多方法没有实现。

关于 web cam 使用自家的摄像头实现 视频捕捉技术 高级篇

asic Capture Operations

Capture Windows

Capture Drivers

Capture Driver Preview and Overlay Modes

Capture Driver Video Dialog Boxes

Audio Format

Video Capture Settings

Capture File and Buffers

Directly Using Capture Data

Capture from MCI Device

Manual Frame Capture

Still-Image Capture

Advanced Capture Options

Working with Palettes

Yielding to Other Applications

AVICap Callback Functions

关于 web cam 使用自家的摄像头实现视频捕捉技术高级篇