| With the explosive growth of the Internet and increasing demand for Multime- dia information transmission on the web, tremendous attention had been attached to the information and technology field. How to enhance the quality of video that transmitted on the net to meet the requirements of QOS makes more sense.There are two methods to transmit the audio and video data on Internet, one is download method and the other is streaming method. Generally A/V file is very so larger that it needs more strong storage capacity. Meanwhile because of the restriction of the bandwidth, it will spend long time to download the file so this process method takes a serious delay problem. The method of streaming transmission avoids the defect that the customers must download all the files to enjoy it. With the way of "downloading and transmission at the same time", it will take you several seconds to decode the files on your client and then you can play it, the rest files will transmitted from the server on the background. It has a widely definition of streaming transmission, now it is mainly means the generally meaning of transmission of media data through Internet, it's special meaning is to transmit the A/V file to PC.TCP/IP protocol is a standard of mutual connection and communication of asynchronous network. On the TCP system, you can expand your application. But the TCP/IP protocol is hardly to adapt multimedia communication unique, especially to meets the needs of consecutive streaming media communication. The Real-time Transport Protocol and the Real-time Transport Control Protocol are designed for the transmission of multimedia data. Besides the function to carry any real-time data, the RTP can also rectify the sequence of the IP package which is transmitted on the IP net. The RTCP is used to carry the feedback information of the transmission quality. The cooperation of RTP and RTCP can optimize the quality of transmission with the least losing, so it is more appropriate to transmit the real-time data.With development of System On Chip of micro-electronics technology, the embedded system based on ARM core have comprehensive application in many filed, Such as communications, network, industry control, instruments, information Electrical appliances and consumed Electrical commodity. As a global provision manufacturer of 32/16 bit embedded RISC MPU solution, the ARM Company produces the ARM serials architecture and becomes the RISC standard in the SOC chip manufacture. The embedded system has attached more importance to our life today. It is a trend to combine the streaming media technique with embeded system. Now, CD, MD, MP3 become the daily life facility, but they all stay on the phase that play the media data themself, if we can apply the streaming media technique on the embeded device, it will be a revolution on multimedia filed. So it is meaningful and have a widely development space to combine the streaming media technique with embeded system.There is a widely requirement for multimedia technology to be applied on embedded system.This dissertation set up an audio system based on embedded Linux system which use the S3C2410 embedded processor and UDA1380 audio process chip. It has realized the recordation of audio data on embedded system and transmission of audio data on Internet. The main construction includes:1 The research of RTP/RTCP protocol: The IETF organization brings forward the RTP protocol. At first this paper introduces the concept and application of Streaming media and exhaustive explain the format of RTP/RTCP pocket and the control regulation of transmission of RTP. There is also an analysis of the QOS problems of multimedia transmission on Internet and it has introduced some common ways to settle them;2 The design of the send part software on embedded Linux and the receiver part software on Linux: The send part of streaming media is set up on embedded Linux system, it utilize the RTP/RTCP lib to realize the transmission of audio data on Internet. It use the software ulaw encode ways to encode the audio data instead of the hardware encode ways. The system is run on the embeded system, so the program needs to run on it. It has some differents with the nomal concept that develop program on PC. In this paper, it has also introduced how to set up a cross-compile environment for embeded system and how to transplant the code on the embeded system. For the receiver part, we use popular VLC streaming media software which can play the received audio data. The VLC software can decode many formats of the multimedia data and also can be a server to stream the multimedia data with unicast or multicast method on Internet; 3 The implementation of audio record on embedded system: It contains the design of application layer and the design of driver layer. For the application layer, it has the function to read the command line to control the time that how long the system will record the audio data and when the system record audio data it is also save the data on it. This paper had detailed introduced the structural of Linux cornel and how to design a driver program on Linux. This system enhance the process speed of audio data with the DMA transmission and subsection buffer mechanism, it has achieved a nice real-time goal. The communication of audio chip UDA1380 and the processor S3C2410 is through the IIC bus and the IIS bus. The IIC bus answer for the initialization of UDA1380 and the IIS bus is responsible for the audio data transmission between the two chips. Firstly the audio data was transmitted from UDA1380 to S3C2410 and the data was received by the IIS revive buffer, and then the data was transmitted to the memory buffer by the DMA channel.The results of this experiment proved that the system has realized recordation and transmission of audio data, and the audio data can be played on the client which is added in the cast group. The design of this system is not only the research and application of net transmission technology but also a meaningful try for the application of embedded Linux technology. It has found a well basement for the next research. This system can be extended as an audio conference and an audio surveillance system. |
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