Weak current College】 【streaming media technology in video conference application-in - Power By】 【China power house network.

<br> IT technology development in all aspects affecting people's work and life. Used to be expensive and complicated remote image communication from us. In recent years talking about the growing number of videoconferencing and streaming media is the image communication technology application of the two. .So, what is between them and the different links? we from both technical and application for analysis. Meeting TV technology and application Conference TV development nearly 20 years of history. As part of a public communications network, its technology fully established in ITU (ITU .-T) / Ministry of information industry norms, we often say H.320/H.323/H.324 series standards. Standards-compliant means that different manufacturers, different types of devices can communicate as if we call and do not consider the .other side of what type of phone. Technically, it includes image sound compression (H.261 or H.263/G.7xx), call control (H.230/H.242/H.245), the data frame structure ( .H.221/H.225), multipoint meetings and management (H.231/H.243), etc. Generally speaking, it has the following characteristics: 1. Compatibility: standards-compliant devices can exchange mutual control. 2. bi .-directional interaction: provides point-to-point or point-to-multipoint-full bi-directional audio and video communications to meet the needs of the two-way exchange. 3. real-time: minimize audio and video transmission delay, so .that the participants have the feeling of being there. Practical application of the General magnitude in milliseconds. 4. supports multiple transport network: such as ISDN, DDN, fibre, microwave, satellite, ATM, frame relay, LAN, etc. 5. sophisticated .call control: the control reference telephone switching network signaling (Q.931/I.400) so that domestic and even international video conference a reality. 6. specialized definition Conference Management: H.243 defines a multipoint Conference of President of control functions, .h.281remote camera remote control, in H.323 Gatekeeper H.225.0 defined (Gatekeeper), all for the remote, massive, multiple network TV conference management. 7. occupied bandwidth: Although the proprietary session TV Terminal mostly support 64K-1920K bandwidth .for audio and video transmission, but in order to guarantee a certain quality, generally require a certain proprietary bandwidth. This has also led to the implementation costs of videoconference. 8. hardware-based decoder (Codec): the high cost. So, based .on the above characteristics, main Conference TV real-time, two-way interactive face-to-face audio and video communication. Its main customers include government departments of the Executive Council, emergency communication, distance learning, telemedicine; enterprise or between enterprises in .Commerce and Engineering Conference, and so on. Streaming media technology and application streaming technology with the Internet (Internet) and the development of rapid development. Unlike a communication-based and starting point of the meeting of the TV technology, streaming media source and computer .and network technologies. Therefore, the streaming media technology is a company, the company Union or trade association's standards. Like Microsoft's Windows Media, RealNetworks' Real System, Apple's QiuckTime, Cisco's IP / TV, etc. Lack of standards, is not compatible with .each other and not entirely a bad thing. As in recent years the development of Internet technology, fierce competition results of a large number of simple, practical and inexpensive new technology and rapidly accepted by the public, such as the Internet, as well as to .its-based streaming media technology. Let's take a look at some features of streaming media technology. 1. streaming media technology is how low-bandwidth, high latency, non-reliable Internet transmission data volume is large audio and video signals. For example, .we hope that through the Internet on a film, there are two ways that A). the full download to a local play again, this may take several hours. B). the side of the download at the side of the playback buffer to reduce .network latency and jitter on playback. The latter is the original idea of streaming media. 2. a streaming media system including audio and video capture and compression, data storage or play, the client receives three parts. As shown in Figure 1: Figure 13 .. In the audio and video capture and compression coding side, through the appropriate hardware or software, analog audio and video signals converted to prepare for transmission or storage of the data format. In addition to meeting-TV H.261/H.263 identical .to discrete Yu-transform (DCT) and predictive coding-based compression algorithm, the streaming media application also adopted in recent years new techniques of image compression, such as RealNetworks of wavelet transform (Wavelet), Windows Media encoding based on the MPEG4 etc. .They are in the low bit-rate by offering better image encoding results. 4. after compression of audio and video data through audio and video playback / storage servers for broadcast and on-demand or storage. This is a streaming media technology features and key .. One technique is to cache. When real-time, continuous tone video signal through non-real-time, packet switching, asynchronous Internet, will result in delay, jitter, and packet loss, will cause the image to a halt, staccato, .and other errors. By buffering technique, first to receive a certain time of audio and video signals are stored in the buffer, and then begin playing while continuing to receive subsequent data. To overcome network latency, jitter, or temporary congestion. In addition, .the transmission using TCP / IP user datagram / real-time Transport Protocol (UDP / RTP), improving transport efficiency. 5. on the client side, the user through the appropriate decoder to receive audio / video stream. The majority of software implementation. .As Microsoft's MediaPlayer, RealPlayer, RealNetworks'. Cheap or even free client software is streaming media application for another characteristic, is the rapid popularization of a cause. Summing up the above characteristics, we can draw the following conclusions: 1. Streaming media technology applied .and from low-speed (28.8K) of the Internet to the high speed (10/100M) Ethernet, fast Ethernet. 2. based on the cache technology of streaming media is basically the quasi real-time transmission, that is, the lower .the network request is to increase the delay. Currently, this time delay, generally within seconds of magnitude. This is a one-way broadcast is not aware of, but on two-way communication will be inconvenienced. 3. to present the computer processing .power, you can implement software for audio and video decoding. This determines the client receive costs can be very low. Which broadcast features also decides the technology on the client's number is unlimited. This greatly reduces the cost of the entire system. 4. with .the network technology and the development of streaming media technology, streaming audio and video quality has been greatly improved. There have been a two-way interactive, multi-point interactive streaming media applications. However, that the client must also be equipped with expensive, .based on dedicated hardware encoder. So, the above client low cost advantage will be affected. 5. application of streaming media has been involved in all aspects. Such as government departments, enterprises of the multimedia information publishing on the Internet; on live video and .audio; video; TV; online advertising network; distance learning; telemedicine, etc. In view of the characteristics of streaming media technology and the successful applications, many traditional Conference TV manufacturers have also introduced a streaming media products, together with conferencing system provides the .user with a more complete solution, and achieved a successful application. Figure 2 is the VTEL Meiguoshixungongsi Turbocast diagram of the streaming media system. Figure 2 it includes: 1. Streaming Media Studio it in real time to encode the image, sound, and the .encoded information transmitted to the network of repeaters, is installed in a normal PC or video conferencing Terminal coding software. 2. the streaming media links this is installed on a network server software, Studio processing audio and video streams via repeaters to broadcast to other repeaters .or end users. Same network can have multiple repeaters, to adapt the structure of the network and to support more end users. 3. the user-side player a Java applet. When you access a site to watch streaming media, the program will automatically .download to the user's Terminal. Therefore, the viewer can in Microsoft IE and Netscape Navigator and other browsers to view media streams directly, without having to download additional software. The system supports real-time broadcasting or online ordering. When the TV Conference through streaming .media system is a real-time broadcast meeting content to an intranet or the Internet. Authorized user you can receive meeting through PC content or Conference on-demand storage on the server session. It brings real-time, bi-directional, high-quality .videoconferencing and easy to implement, flexible, low-cost stream media organic combination to meet user demand in many areas, in practice achieved very good results. Summing up, as video communications technologies applications, videoconferencing and streaming media technology and applications have many similarities, .but there are many different. Conferencing as a full-fledged communication system that provides real-time, bidirectional, multiple network, wide area and guarantee the quality of audio and video communications; and as the new technology of streaming media to a low-cost ., efficient, easy-to-use audio and video communication practices, as well as the foreseeable development of its update. From the application perspective, learn about videoconferencing and streaming media features and different point, according to user needs both organically combined, will be .a perfect solution..