| After the birth of telephone,people want to see the face of whom they are talking with.But the technology and the finance status limit this willing.Now with the developing of modern science and technology and the improve of living level,the time to develop video-phone is coming.Video-phone also can be a cheap endpoint of video-conference which is help to solve the problem that incleasing conferences cost more and more money and time.And video-conference is becoming popular after "9.11" because it can avoid the threat of journey.Video-phone and video-conference industry is moving quicky.One of the important pulse is the recommendation maded by ITU.ITU made a series of recommendation including multidedia codec and control signal so any of equipment produced by any of companies can communicate each other.The video-phone we design is based on IP network,because IP network is wide-spread and is spreading now and it can provide wide band which is important to guarantee the quality of communication.The corresponding protocol of ITU is H.323.The main processor we use is TM1300 produced by Philips Co.TMlSOO has a lot of advantages such as it has VLIW which is suited to processing multimedia data and it also have a convenient developing tool.Using TM1300 we only need few chips to implement our video-phone system.The main difficulty of video-phone is real time implement of A-V codec,real time transmit of A-V data over IP,implement of H.323 protocol stack,and so on.This article is mainly about this difficulty point,with some necessary introduce of background knowledges such as the technology of A-V compress and H.323 protocol.In the first chapter,we present the developping history and the situation of video-phone.The next chapter,introduces H.323 protocol stack. The third chapter introduces A-V compress technology and standard,mainly about audio compress.The following two chapters are the most important. The fourth chapter is about how to realtime implement of audio codec in TM1300.After we optimize the code,we real time implement G.723.1 and G.729A low bitrate voice codec.The fifth chapter discusses another important technology:real time transmit A-V data over IP network.We use C program language implemented RTF and we discusses the performance of RTP. At the last chapter,we summarize our experience and give a prospect of video-phone system,we wish this can help the future developers. |
