【作者】 胡浩；

【导师】 李华；

【作者基本信息】 天津大学 ， 信号与信息处理， 2007， 硕士

【摘要】 IP多媒体子系统(IMS)是目前业界公认的多媒体业务控制和网络融合平台。其意义在于实现终端用户业务的融合,使得运营商更灵活地定制用户业务,用户可以方便在不同的应用和网络之间自由切换,实现固定网络和移动网络的融合。本文中开发的多功能视频转换编码系统是一款基于飞思卡尔MSC8122 DSP平台的嵌入式多通道视频转换编码解决方案,应用于IMS媒体网关中,提供多路、兼容H.264, H.263和MPEG-4多种视频格式的实时转换,能根据实际要求实现图像码率、帧率和空间分辨率的转换。本论文首先对目前的视频转换编码技术进行综述性介绍,然后给出了系统架构的选择以及重要模块描述,改进了时域转码的宏块模式映射算法。最后,对转码系统的优化进行了详细讨论。本文的主要贡献有:1、提出了一种基于FDVS算法的改进的模式映射算法,该算法有效的减少了由于模式误判导致转码器编码端编码图像质量的下降的问题。目前已经应用于转码系统中。2、提出了一种小数像素运动估计快速算法。该算法具有良好的通用性。试验结果表明,该算法在保证编码图像质量的同时,编码速度大为提高。3、本文中的转换系统实现多路实时转码。MSC8122 DSP在400MHz的主频下,对于CIF格式的输入码流,每秒最快能转码404帧H.263到H.263的图像,最慢能转173帧H.264到H.264的图像。更多还原

【Abstract】 IP Multimedia Subsystem (IMS) is a widely recognized platform for multimedia service and for internet adaptation. Such system can offer the operators flexibility in providing services and the end users convenience in switching between different networks and applications.The Multi-role Video Transcoding System presented in this paper is a versatile Freescale MSC8122DSP based video transcoder resolution, with support for H.263, MPEG-4 and H.264 standards. It can perform bit-rate transcoding, frame-rate transcoding and resolution downscaling at the request of users and at high channel density. The system is about to be used in IMS media gateway.Firstly, this paper makes an overview of recent proposed video transcoding technology. Secondly, this paper presents the architecture of video transcoding system and its key modules. Thirdly, an improved Macroblock mode-mapping algorithm is proposed. And lastly, details about the optimization are discussed.The three major innovations are as follows.①Presents an improved mode-mapping algorithm based on FDVS, which can effectively improve the temporal transcoding quality. The algorithm has been integrated into the transcoder successfully.②Proposes a novel fast sub-pixel motion estimation algorithm. This algorithm can speed up encoding dramatically without severe video quality degradation.③The transcoder can perform at high channel density in real time. For CIF bitstream, the MSC8122DSP can transcode 404 frames for H.263 to H.263 and 173 frames for H.264 to H.264 at 400MHz frequency.更多还原