A Platform-independent Implementation Study Of Audio Streaming Media In Embeded System

With the rapid growing of network technology, multimedia technology and micro-electronics technology, the application of streaming media in the network has been great developed. People are dissatisfied with the unitary type of media in the work and daily life. For the advantages of Streaming media, such as , speediness and lifelikeness, it has been widely applied in a series of departments, companies and people's lives. Also ,with more and more embedded portable devices has the capability to access networks, more and more people has the aspire to enjoy audio and vedio information through those devices and the less-cost Internet .In this paper, three key technologies have been studied , digital audio encoding/decoding technology, real-time transport protocol and buffer technology. With those technologies , a digital broadcast system ,which is based on streaming media technology and IP multicast technology , is designed . This system is consisted of one streaming server and numbers of streaming players.Based on the careful reasearch on digital audio signal, MP3 file ,which has high qulity tone and high compression ratio, finally become the audio format that can be processed and transport by this system .According to the chraracters of streaming media transport , such as ,low transport delay and certain packet-lost fraction , UDP is finally chosen to be the network transport layer protocol. About the streaming media protocol,we have collected many standards . And afer careful comparation, the RTP/RTCP protocol is finally taken as the most proper one for our system. When be used, it is predigested. Also, in this system, congestion control mechanism is applied. We use the RTCP report from the receiver to estimate the network congestion status, and AIMD algorithm to adjust the packet transmit rate. Because of sudden packet decrease will result in the unsteadiness of the receiver part, smooth adjustment should be considered , here , slow increase and decrease has been adoptted.When the streaming server and streaming player are implemented, JAVA language is used .Both of them are based on the J2ME. Further , we choose the CDC configuration after careful contrast between CDC and CLDC , for the server and player need to steadily access to network . When coding , the classes in Foundation Profile are used , which are the core of CDC class. For the player, hardware decoder is adopted in order to increase the realtime capability of the device. JNI technology can help to realize the seemless combination of JAVA code and native code.At the end of this paper, some tests has been described ,also the emphasis of the further work has been introduced .