点对点视频会议程序:VideoNet

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();

解码器：

这是tmndecoder(H.263解码器)的修改版。使用ANSI C编写，我将它转换到C++使其方便在Windows应用程序中使用。我移除了一些用于显示和文件处理的文件，移除了不必要的代码并增加了一些新文件。

原始的库中一些文件不适合于实时的解码。我已经做了修改使其适合实时的解码处理。现在，可以使用该库来解码H263帧，该库非常快，性能不错。

解码的使用方法：

//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。