VideoNet

• Download source - 155 Kb
• Download demo - 109 Kb

Introduction

This application allows any 2 persons on the LAN/Intranet (possibly Internet too) to have video conference. There are several video conference applications existing today. Each has its own performance enhancement techniques. The major problem in video conference is that the size of video frames is too big for transmission. Hence the performance is based on the codec used for encoding and decoding the frame. I am using Fast h263 Encoder library which gives better compression rate at high speed. This application can also be used on the Internet with little modification.

Recording and Playing Audio

I have used the same RecordSound and PlaySound classes which I have used in my previous voice conference application. Here, I will provide a brief overview of how to use this RecordSound and PlaySound classes.

// 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 OnSoundData 

// callback function of 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);

Video Capture

Video capture is done using VFW (Video For Windows) API. It provides support for capturing the video from web cam. VideoCapture.h and VideoCapture.cpp are the files which contain the code for complete video capture process.

Here are the brief details of how to use this class....

// Create instance of Class 

vidcap=new VideoCapture(); 

// This is later used to call display function of 

// main dialog class when the frame is captured... 

vidcap->SetDialog(this); 


// This does lot of work including connecting to driver 

// and setting the desired video format. Return TRUE if 

// successfully connected to videocapture device. 

vidcap->Initialize(); 


// If successfully connected then you can get BITMAPINFO 

// structure associated with video format. This is later 

// used for displaying the captured frame... 

this->m_bmpinfo=&vidcap->m_bmpinfo; 

// Now you can start the capture.... 

vidcap->StartCapture(); 

// Once capture started frames will arrive in callback function 

// "OnCaptureVideo" of VideoCapture class.Here you call display 

// function to display the frame. 


// To stop the capture 

vidcap->StopCapture(); 

// If your job is over....just destroy it.. 

vidcap->Destroy();

If you do this much work, your code will compile well....but linker will trouble you. You must link the suitable libraries....

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

Displaying the Captured Video Frame

There are various methods and APIs for displaying the captured frame. You can use SetDIBitsToDevice() method to directly display the frame. But this is quite slow as it is based on Graphics Device Interface (GDI) functions. The better method is to use DrawDib API to draw the frame. The DrawDib functions provide high performance image-drawing capabilities for device-independent bitmaps (DIBs). DrawDib functions write directly to video memory, hence provide better performance.

Here is the brief view of how to use DrawDib API to display frame:

// Initialize DIB for drawing... 

HDRAWDIB hdib=::DrawDibOpen(); 

// Then call this function will suitable parameters.... 

::DrawDibBegin(hdib,...); 

// Now if you are ready with frame data just 

// invoke this function to display the frame 

::DrawDibDraw(hdib,...); 

// Finally termination... 

::DrawDibEnd(hdib); 
::DrawDibClose(hdib);

Encoder and Decoder Library

Encoder

I have used fast h.263 encoder library for the encoding. This library was the modified version of Tmndecoder to make it more faster for real time encoding. I have converted this library from C to C++ so that it can be integrated into any Windows application easily. I have removed some of the unnecessary codes/files from the fast h263 library. Also moved definitions and declarations in their proper .h and .cpp files.

Brief view of usage of H263 Encoder library

// Initialize the compressor 

CParam cparams; 
cparams.format = CPARAM_QCIF; 
InitH263Encoder(&cparams); 


//If you need conversion from RGB24 to YUV420 then 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 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 callback function 

// that you have registerd at the begining... 


// Finally terminate the encoder 

// ExitH263Encoder();

Decoder

This is the modified version of tmndecoder (H.263 decoder). It was in ANSI C. I have converted it into C++ so that it can be integrated into any Windows application. I have removed some of the files which had display and file storing functions. I have removed the unnecessary code and also added some new files.

Original library dealt with files. It was not suitable to use for real time decoding. I have done some major changes so that it can be easily integrated into the application for real time decoding process. Now one can use this library for decoding H263 frames. This library is quite fast and gives better performance.

Usage of Decoder .....

//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();

How to run the application

Copy the executable file into 2 different machines A & B which are on LAN. Run both the applications. From machine A (or B), select Connect menu item, and in the popup dialog box, enter the name or IP Address of the other host (B), and press Connect button. In the other machine (B), Accept/Reject dialog box will appear. Press Accept button. In the machine A, notification dialog box will get displayed. Press OK to begin the conference.

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

Acknowledgement

I likes to thank Paul Cheffers for his audio recording and playing sound classes. You are seeing this videonet application here....it is because of Open Source libraries contributed by open minded persons. I am grateful to the developer Karl Lillevold of Tmndecoder and Roalt Aalmoes of h.263 fast encoder library for making it free.

If you have any queries or suggestions, please feel free to mail me at nsry2002@yahoo.co.in.