📄 点对点视频会议程序videonet开发例解-太平洋电脑网pconline-[vc-mfc].htm
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<P> <A
href="http://www.pconline.com.cn/pcedu/empolder/gj/vc/0508/acc/VideoNet_src.zip">下载源代码</A>。</P>
<P><IFRAME id=ad_top name=ad_top align=left marginWidth=0
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frameBorder=0 width=320 scrolling=no
height=280></IFRAME> 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。</P>
<P><STRONG>音频的录制与播放</STRONG></P>
<P> 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。</P>
<P>// Create and Start Recorder Thread<BR>
record=new RecordSound(this);<BR>
record->CreateThread();<BR><BR><BR>// Create and Start
Player Thread<BR> play=new
PlaySound1(this);<BR>
play->CreateThread();<BR><BR><BR>// Start
Recording<BR>
record->PostThreadMessage(WM_RECORDSOUND_STARTRECORDING,0,0);<BR><BR><BR>//
Start Playing<BR>
play->PostThreadMessage(WM_PLAYSOUND_STARTPLAYING,0,0);<BR><BR><BR>//
During audio recording, data will be available in the
OnSoundData<BR>// callback function of the RecordSound class.
Here, you can place<BR>// your code to send the data to remote
host...<BR><BR><BR>// To play the data received from the
remote host<BR>
play->PostThreadMessage(WM_PLAYSOUND_PLAYBLOCK,size,(LPARAM)data);<BR><BR><BR>//
Stop Recording<BR>
record->PostThreadMessage(WM_RECORDSOUND_STOPRECORDING,0,0);<BR><BR><BR>//
Stop Playing<BR>
play->PostThreadMessage(WM_PLAYSOUND_STOPPLAYING,0,0);<BR><BR><BR>//
At last, to Stop the Recording Thread<BR>
record->PostThreadMessage(WM_RECORDSOUND_ENDTHREAD,0,0);<BR><BR><BR>//
To stop playing thread...<BR>
play->PostThreadMessage(WM_PLAYSOUND_ENDTHREAD,0,0);</P>
<P><STRONG>视频捕获</STRONG></P>
<P> 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。<BR><BR> 如下代码说明了如何使用该类：</P><PRE>// Create instance of Class<BR> vidcap=new VideoCapture();</PRE><PRE><BR>// This is later used to call display function of the main<BR>// dialog class when the frame is captured...<BR> vidcap->SetDialog(this);</PRE><PRE><BR>// This does lot of work, including connecting to the driver<BR>// and setting the desired video format. Returns TRUE if<BR>// successfully connected to videocapture device.<BR> vidcap->Initialize();</PRE><PRE><BR>// If successfully connected, you can get the BITMAPINFO<BR>// structure associated with the video format. This is later<BR>// used to display the captured frame...<BR> this->m_bmpinfo=&vidcap->m_bmpinfo;</PRE><PRE><BR>// Now you can start the capture....<BR> vidcap->StartCapture();</PRE><PRE><BR>// Once capture is started, frames will arrive in the "OnCaptureVideo"<BR>// callback function of the VideoCapture class. Here you call the<BR>// display function to display the frame.</PRE><PRE><BR>// To stop the capture<BR> vidcap->StopCapture();</PRE><PRE><BR>// If your job is over....just destroy it..<BR> vidcap->Destroy();</PRE>
<P> 要使以上代码通过编译，你应该链接适当的库：</P>
<P>#pragma comment(lib,"vfw32")<BR>#pragma
comment(lib,"winmm")</P>
<P><STRONG>显示捕获的视频帧</STRONG><BR><BR> 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。<BR><BR> 以下代码摘要演示了使用DrawDib
API显示视频帧。</P><PRE>// Initialize DIB for drawing...<BR> HDRAWDIB hdib=::DrawDibOpen();</PRE><PRE><BR>// Then call this function with suitable parameters....<BR> ::DrawDibBegin(hdib,...);</PRE><PRE><BR>// Now, if you are ready with the frame data, just invoke this<BR>// function to display the frame<BR> ::DrawDibDraw(hdib,...);</PRE><PRE><BR>// Finally, termination...<BR> ::DrawDibEnd(hdib);<BR> ::DrawDibClose(hdib);</PRE>
<P><STRONG>编解码库<BR></STRONG><BR> 编码器： </P>
<P> 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。<BR>以下是H263编码库的使用方法：</P><PRE>// Initialize the compressor<BR> CParam cparams;<BR> cparams.format = CPARAM_QCIF;<BR> InitH263Encoder(&cparams);</PRE><PRE> </PRE><PRE>//If you need conversion from RGB24 to YUV420, call this<BR> InitLookupTable();</PRE><PRE> </PRE><PRE>// Set up the callback function<BR>// OwnWriteFunction is the global function called during<BR>// encoding to return the encoded data...<BR> WriteByteFunction = OwnWriteFunction;</PRE><PRE> </PRE><PRE>// For compression, data must be in the YUV420 format...<BR>// Hence, before compression, invoke this method<BR> ConvertRGB2YUV(IMAGE_WIDTH,IMAGE_HEIGHT,data,yuv);</PRE><PRE><BR>// Compress the frame.....<BR> cparams.format = CPARAM_QCIF;<BR> cparams.inter = CPARAM_INTRA;<BR> cparams.Q_intra = 8;<BR> cparams.data=yuv; // Data in YUV format...<BR> CompressFrame(&cparams, &bits);</PRE><PRE><BR>// You can get the compressed data from the callback function<BR>// that you have registerd at the begining...</PRE><PRE><BR>// Finally, terminate the encoder<BR>// ExitH263Encoder();</PRE><STRONG>解码器：</STRONG><BR><BR> 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。<BR><BR> 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。<BR><BR> 解码的使用方法：<PRE>//Initialize the decoder<BR> InitH263Decoder();</PRE><PRE><BR>// Decompress the frame....<BR>// > rgbdata must be large enough to hold the output data...<BR>// > decoder produces the image data in YUV420 format. After<BR>// decoding, it is converted into RGB24 format...<BR> DecompressFrame(data,size,rgbdata,buffersize);</PRE><PRE><BR>// Finaly, terminate the decoder<BR> ExitH263Decoder();</PRE>
<P><STRONG>如何运行程序</STRONG></P>
<P><STRONG> </STRONG>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。<BR><BR>That's
it....Enjoy......!!! <BR><BR><STRONG>致谢：</STRONG><BR><BR> 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。<BR><BR> 如果你有任何问题或建议，可以发邮件给我
nsry2002@yahoo.co.in</P><BR clear=all>
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