点对点视频会议程序VideoNet开发例解

　　下载源代码。

　　该程序可以用于两个人在LAN/Intranet(或者Internet)上进行视频会议。现在有许多视频会议程序，每个都有各自的性能提升技术。主要的问题是视频会议视频帧的尺寸对于传输来说太大。因此，性能依赖于对帧的编解码。我使用快速h263编码库来达到更好的压缩率提高速度。该程序做些小改动也可以在Internet上使用。

音频的录制与播放

　　我在以前的语音会议程序中使用了RecordSound和PlaySound类，这里我将提供摘要说明RecordSound和PlaySound类的使用。

// Create and Start Recorder Thread
   record=new RecordSound(this);
   record->CreateThread();


// Create and Start Player Thread
   play=new PlaySound1(this);
   play->CreateThread();


// Start Recording
   record->PostThreadMessage(WM_RECORDSOUND_STARTRECORDING,0,0);


// Start Playing
   play->PostThreadMessage(WM_PLAYSOUND_STARTPLAYING,0,0);


// During audio recording, data will be available in the OnSoundData
// callback function of the RecordSound class. Here, you can place
// your code to send the data to remote host...


// To play the data received from the remote host
   play->PostThreadMessage(WM_PLAYSOUND_PLAYBLOCK,size,(LPARAM)data);


// Stop Recording
   record->PostThreadMessage(WM_RECORDSOUND_STOPRECORDING,0,0);


// Stop Playing
   play->PostThreadMessage(WM_PLAYSOUND_STOPPLAYING,0,0);


// At last, to Stop the Recording Thread
   record->PostThreadMessage(WM_RECORDSOUND_ENDTHREAD,0,0);


// To stop playing thread...
   play->PostThreadMessage(WM_PLAYSOUND_ENDTHREAD,0,0);

视频捕获

　　使用VFW(Video For Windows)API进行视频捕获，它提供了通过webcam进行视频捕获。VideoCapture.h 和VideoCapture.cpp包含了处理视频捕获的代码。

　　如下代码说明了如何使用该类：

// Create instance of Class
   vidcap=new VideoCapture();

// This is later used to call display function of the main
// dialog class when the frame is captured...
   vidcap->SetDialog(this);

// This does lot of work, including connecting to the driver
// and setting the desired video format. Returns TRUE if
// successfully connected to videocapture device.
   vidcap->Initialize();

// If successfully connected, you can get the BITMAPINFO
// structure associated with the video format. This is later
// used to display the captured frame...
   this->m_bmpinfo=&vidcap->m_bmpinfo;

// Now you can start the capture....
   vidcap->StartCapture();

// Once capture is started, frames will arrive in the "OnCaptureVideo"
// callback function of the VideoCapture class. Here you call the
// display function to display the frame.

// To stop the capture
   vidcap->StopCapture();

// If your job is over....just destroy it..
   vidcap->Destroy();

　　要使以上代码通过编译，你应该链接适当的库：

#pragma comment(lib,"vfw32")
#pragma comment(lib,"winmm")

显示捕获的视频帧

　　有许多方法和API可以显示捕获的视频。你可以使用SetDIBitsToDevice()方法直接显示，但给予GDI的函数非常的慢。更好的方法是使用DrawDib API 显示。DrawDib函数为设备无关位图(DIBs)提供了高性能的图形绘制能力。DrawDib函数直接写入视频内存，因此性能更好。

　　以下代码摘要演示了使用DrawDib API显示视频帧。

// Initialize DIB for drawing...
   HDRAWDIB hdib=::DrawDibOpen();

// Then call this function with suitable parameters....
   ::DrawDibBegin(hdib,...);

// Now, if you are ready with the frame data, just invoke this
// function to display the frame
   ::DrawDibDraw(hdib,...);

// Finally, termination...
   ::DrawDibEnd(hdib);
   ::DrawDibClose(hdib);

编解码库

　　编码器：

　　我使用快速h.263编码库进行编码。该库是使其实时编码更快的 Tmndecoder 修改版。我已经将该库从C转换到C++，这样可以很容易用于任何Windows应用程序。我移除了快速h263编码库中一些不必要的代码与文件，并在.h和.cpp文件中移除了一些定义与申明。
以下是H263编码库的使用方法：

// Initialize the compressor
   CParam cparams;
   cparams.format = CPARAM_QCIF;
   InitH263Encoder(&cparams);

//If you need conversion from RGB24 to YUV420, call this
   InitLookupTable();

// Set up the callback function
// OwnWriteFunction is the global function called during
// encoding to return the encoded data...
   WriteByteFunction = OwnWriteFunction;

// For compression, data must be in the YUV420 format...
// Hence, before compression, invoke this method
   ConvertRGB2YUV(IMAGE_WIDTH,IMAGE_HEIGHT,data,yuv);

// Compress the frame.....
   cparams.format  = CPARAM_QCIF;
   cparams.inter   = CPARAM_INTRA;
   cparams.Q_intra = 8;
   cparams.data=yuv;    //  Data in YUV format...
   CompressFrame(&cparams, &bits);

// You can get the compressed data from the callback function
// that you have registerd at the begining...

// Finally, terminate the encoder
// ExitH263Encoder();

//Initialize the decoder
   InitH263Decoder();

// Decompress the frame....
// > rgbdata must be large enough to hold the output data...
// > decoder produces the image data in YUV420 format. After
//   decoding, it is converted into RGB24 format...
   DecompressFrame(data,size,rgbdata,buffersize);

// Finaly, terminate the decoder
   ExitH263Decoder();

如何运行程序

　　拷贝可执行文件到局域网上两台不同的机器中：A和B，运行他们。在机器A(或B）中选择connect菜单条，在弹出的对话框中输入机器B的名字或IP地址然后按connect按钮，在另外一台机器（B）显示出accept/reject对话框，按accept按钮。在机器A将显示一个通知对话框，按OK后开始会议。

That's it....Enjoy......!!!

致谢：

　　我感谢 Paul Cheffers 提供了他的音频录制播放类。因为有了开源人士奉献的开源库才有你所看到的videonet程序，我感激Tmndecoder的开发者Karl Lillevold和h.263快速编码库的开发者Roalt Aalmoes 免费提供这些开发库。

　　如果你有任何问题或建议，可以发邮件给我 nsry2002@yahoo.co.in