Research On Dynamic Multi-Rate Transcoding For Mobile Streaming Media

With the development of mobile communication technology, the speedup of mobile network connection, the intelligentization of mobile devices, and the improvement of digital compression technology, mobile devices have been not only the simple tools for communication, but also intelligent platforms for multimedia. Meanwhile, users have been dissatisfied with simple value added services, such as MMS, downloading of picture and ring etc. The emergence of mobile streaming media greatly changes the situation for it provides services including VOD, video communication and video surveillance over wireless channels. Mobile streaming media is the combination of mobile communication and streaming media transmission. It transmits data through mobile network using streaming media technology over mobile devices. However, the diversity of terminal users, the volatile wireless network and the limited computational power on mobile devices all limit the development of mobile streaming media. So we need to research some technologies to solve these problems.Bit-rate reduction transcoding can provide corresponding bit-rate video streams according to the computational power of the mobile terminals and the bandwidth of network. So it is the key technology to solve these problems. The most straightforward way to achieve this is to use cascaded pixel-domain transcoding architecture, which decodes the video bit stream and fully reencodes the reconstructed signal at the new rate. The best performance can be achieved by this approach. However, it is quite costly. In open-loop transcoding architecture, the quantized coefficients are inverse quantized and then simply requantized to satisfy the new output bit rate. Significant complexity is saved. However, drift is generated by the loss of high frequency data. So the research of bit-rate reduction transcoding is to find a good balance in the tradeoff between complexity and quality. Moreover, the diversity of mobile terminals requires generating video streams with different bit-rate. The existing transcoders need to transcode once for each target streaming with heavy workload and poor flexibility. Therefore, we need to design a new transcoder for mobile streaming media.In order to meet the needs of mobile streaming media, we present a novel bit-rate reduction technology: Dynamic Multi-Rate Transcoding technology. Its core idea is using MV information based closed-loop FGS transcoder to generate a base layerstreaming which can be decoded singly and an enhancement layer which can be truncated at any desirable number of bits to support continuous bit-rate scalability. Through this way, transcoding only needs once to generate various target bit-rate streams. Meanwhile, in order to work properly in volatile wireless network, a network adaptive dynamic transcoding algorithm is proposed. RTCP feedback packet is analyzed to diagnose the network, and the output bit-rate is dynamically adjusted. In addition, the decoding part of the FGS transcoder is optimized, and the decoding performance is substantially increased. Experimental results show that the Dynamic Multi-Rate Transcoding technology fully satisfy the needs of mobile streaming media for its high transcoding speed, good transcoding quality and network adaptive bit-rate dynamically adjustment.Finally, adopting the Dynamic Multi-Rate Transcoding technology, a complete mobile streaming media system is presented.