The Software Design Of Embedded Network Multichannel Audio-Video Server

1. IntroductionThe Multimedia Surveilance System is an interdisciplinary application field emerging research areas such as multimedia data processing, networking, computer vision, artificial intelligence, etc. With the rapid development of computer science technologies, the MSS itself progresses greatly. The first generation of MSS is constructed on tape-based platform and processes analog-signals mainly. Now, the latest MSS is transplanted to computer-based platform and concentrates on digital signals primarily.As the development of Internet, especially the mobile communication and the multimedia realtime communication, people bring forward a more high request. IPv4 emerged many shortcomings. IPv6 inherit the advancement of IPv4, and according to the experience come from IPv4, IPv6 made a great extent modification and function enlargement, it now has a far more powerful function than IPv4.Thus, if we combine the Multimedia Surveilance System and the IPv6 technology, it must have a bright future of application and society value.2. The solution of multichannel MPEG-4 embedded network surveilance systemIn this thesis, we will present a brand-new solution for MSS which using MPEG4 video compression technology and embedded technology. This system is composed of server part and surveilance part. The server part collects the data, transforms it, compression coding and transmits, and manages the interaction with the surveilance part.The surveilance part receives the data, decodes and displays it, stores the data, replays it and sends control messages to server.This system is developed based on high performance ARM embedded processor and embedded linux, supporting both C/S and B/S modes. As to the sensitive data and control information, the user should use the special client software to login, after authenticated, then send and receive data. The user also can use the special client software to set the system, and control the pan&tilt. As to the ordinary data, the user could logins by browser, receives video or watch video.3. The server's hardware platform of multichannel MPEG-4 embedded network surveilance systemThe system is developed based on ARM embedded processor PXA255, which harmonizes the peripheral equipment of SDRAM, Flash, IME6400, MPEG-4 encoding, Lan91C111 network controller, SAA7114 video AD and IDT821024 audio codec, it constructs hardware platform of the server. First , the four channels video stream signals perform A/D conversion and become 8 bits digital signal of 656 format, this signal is provided to FPGA. FPGA cuts down the received video data and converts the data into 601 format. Finally, the data is provided to IME6400 by 27MHz clock. At the same time, based on the audio synchronization signal provided IME6400, FPGA provides 8 bits PCM format audio streams to IME6400. When IME6400 receives all data of one frame, it begins to lie all of them and compress, after that, it tells Xscale processor by interruption mode. The processor read IME6400's special register, it can receive one frame audio stream or video stream data, which is compressed. After that, the processor could send out this frame data by the LAN91C111 Ethernet controller and also write in HDD.4. The realize of server's softwareThe development platform of the the server's software is embedded Linux operating system. At first, we construct cross-compiler environment of ARM platform; transplant blob as terminal booting program; cut down Linux as terminal operating system; consult the interface and timing of the hardware, according to the practical hardware circuit, add and modify drive program; program the start up sequence, cross compiled correlative dynamic storeroom, compile start script and make root file system, complete the conformation of the software platform.The part of Linux operating system's network is used IPv4 and IPv6 dual stacks, provids sustains for the part of network communications of server's softerware. Server's software uses multithreading structure, realizes the reception of surveilance data, local storage, network transmisson and user control function. We use data queue and mutex mechanism between the threads to realize communication and synchronization.5. The realize of client's softwareWe choose a VC+MFC+UI storeroom as an application development platform. In general, the program uses the SDI structure, the system adpots Document to deal with all the data and information, adpots View to display the result to the user, adpots MainFrame to deal with the user's command, then distributes it to the Document or View structure. In order to distribut the task well, the program adopts multithreading structure.The system will use a light protocol which the system defines itself. The funtion is to complete the communication between the client part and the server. The transport of network sustains IP unicasting/broadcasting/multicasting and the combination of them. In order to optimize the performance, and improve the compatibility. 6. ConclusionThe embedded server can perform four channels NTSC/PAL video streams'realtime collection, MPEG4/2/1 compressing, network unicasting/ broadcasting/mu–lticasting and saving into HDD. It also supports four channels audio streams' collection, encoding, network broadcasting and replay. It provides two interview interfaces, special client and universal browser. It is good at universal characteristic.The client software performances four channels realtime MPEG4 video streams' network receiving, decoding replay, video browsing, searching, download and play, the video streams are clear and stabilization, audio streams are smoothly and fluency, video and audio streams' synchronization is well, they are well in matching. The system also supports pan&tilt controlling, joint alarming, user purview validating, dynamic parameter modification etc.