一种基于组播的视频转码系统的设计与实现

视频会议是一种支持人们远距离进行实时信息交流、开展协同工作的应用。基于组播骨干网(MBone)的视频应用已成为研究的热点。目前,在组播视频会议中,视频发送者基本上都是按事先设定的带宽进行数据发送。这种按固定速率发送视频的方式无法同时满足所有接收者对视频质量的要求。该文提出并实现了一个视频转码系统,该转码系统被配置在窄带网络和宽带网络的连接处,一方面接收来自宽带网络的组播视频数据,另一方面能够针对窄带网络的可用带宽对接收到的视频数据进行码率转换,实时降低输出视频的码率并将转码后的视频发送到另一个组播组,使窄带网络上的用户能通过该组播组参与视频会议。     

应急指挥移动监控系统的设计与实现

设计了基于3G的应急指挥移动监控系统,充分利用现代计算机网络和3G移动通信技术,由移动视频采集终端、监控终端、应用服务器等组成的监控系统,实现了与远程指挥中心的实时数据、语音和视频通信。     

视频转码应用分析

在视频会议系统中还有日常拍摄处理视频时,需要利用视频转码技术对传统和新兴视频流进行格式转换。使用转码的意义在于可以在不损失任何视频质量的前提下节省高达50％的网络带宽。转码的分类按照媒体格式可分为音频转码、视频转码,视频转码比较出名的有暴风转码、格式工厂,音频转码用大众的千千静听就能满足使用需要。本文以转码应用为研究对象,进一步分析软件转码技术的应用。     

Ad-hoc 网络中基于实时票选机制的无线视频组播

在Ad-hoc网络应用层提出一个分布式的实时＂票选＂机制,来动态发现并统计网络中各个移动终端当前所处的状态。进而在移动终端上设计并实现一个基于该机制的无线视频组播系统。该系统可以实时调查出不同视频提供者的受欢迎程度,并以此为指导自动向移动用户推送用户可能更感兴趣的无线视频流。网络中每一个移动用户都可以同时作为视频服务器和客户端。     

视频移动终端实时定点与缩放

针对在移动终端自由缩放查看视频细节的需求,提出移动终端的视频图像定点与缩放系统,包含手势识别与越界纠正技术,详细给出了系统框架和系统流程。手势识别给出了单指拖动和双指缩放的检测与坐标转换计算方法,而后对变换参数的取值进行越界纠正和边界限定。系统架构包含视频解码、画面绘制、同步交互,在系统流程及其实现中分别由三个线程并行承载以提高效率。测试结果分析表明,该系统在保留传统视频播放方式上加入了定点与缩放,在播放效率相比传统视频播放方式的损失平均仅占14%的同时,交互响应时间控制在6ms内,最大限度消除了交互引起的画面闪烁和跳帧。系统在资源有限的移动终端上实现了视频播放的实时定点与缩放,有广阔的应用前景,应用价值高。     

基于ARM11的嵌入式无线视频终端的设计

随着无线局域网的广泛应用,为了在嵌入式系统中整合无线局域网宽带通信技术进行视频传输;提出一种基于ARM11硬件平台和嵌入式Linux操作系统的无线视频终端系统的设计方案,给出系统的总体设计和主要功能模块的实现,其中包括视频采集模块、无线视频传输模块的硬件设计,嵌入式Linux的驱动程序移植、H.264数字视频压缩及应用程序实现等;该系统实现了802.11无线局域网内的视频传输,实时监测网络的数据流量和拥塞状况,提高网络传输质量,保证视频播放流畅性,可靠性高且易于使用;实践证明本系统稳定性高,实时性好,运行可靠,可应用于视频监控领域。     

基于DirectShow的无线移动视频监控系统

提出并实现了一种基于微软DirectShow构架的无线移动视频监控系统。系统采用多路IP组播方式通过WLAN传输视频流,移动终端基于WinCE平台。视频服务器端的视频采集和移动终端的实时视频回放是采用DirectShow技术实现的。该系统比传统的有线监控系统具备更强的灵活性和移动性。     

基于Symbian OS的无线视频监控系统

无线视频监控系统是利用现有的无线资源,采用无线收发技术,研制和开发出一套系统。它实现远程监控图像采集和传送,改变传统的短距离有线视频监控的方式。本文设计并实现了一种基于Sym bian OS的无线移动视频监控系统,移动视频采集端与终端基于Series 60平台,移动视频采集端的视频采集和移动终端的实时视频接收是通过连续绘制BMP图像实现。     

基于Sprite的手机移动视频监控系统

为了实时实现监控,文章提出了基于Sprite技术开发手机移动视频监控系统的方案,较详细地介绍了系统的设计与实现,服务器与手机终端之间采用Datagram方式传输图片数据,手机终端采用Sprite技术以动画效果实现实时视频监控。通过实验测试,系统达到了实时视频监控的要求。     

基于H.264标准的无线局域网视频传输系统实现方案

近年来,无线移动终端PDA(personal digital assistant)以其体积小、重量轻、功能完善等诸多特点在移动办公领域发挥了重要作用,而新一代视频编码标准H.264标准的提出又为无线信道等环境下的视频传输提供了更多技术保证.根据H.264编码标准的特点和PDA平台的基本特性,提出了一种无线局域网环境下的视频传输系统方案,该方案采用H.264作为视频编码方法,PDA作为移动终端,RTP/UDP/IP作为网络传输协议,并在此基础上构建了系统的演示平台.测试结果表明,该系统可以在无线局域网环境下实现视频的实时传输,显示帧率10帧/s以上(CIF格式).     

Network-adaptive autonomic transcoding algorithm for seamless streaming media service of mobile clients

As a result of improvements in wireless communication technologies, a multimedia data streaming service can now be provided for mobile clients. Since mobile devices have low computing power and work on a low network bandwidth, a transcoding technology is needed to adapt the original streaming media for mobile environments. However, wireless networks have variable bandwidths depending on the movement of clients and the communication distance from Access Point (AP). These characteristics make it hard to support stable Quality of Service (QoS) streams for mobile clients. In this paper, a target transcoding bit-rate decision algorithm is proposed to provide stable QoS streams for mobile clients. In our experiments, the proposed algorithm provides seamless streaming media services based on the network adaptive bit rate control and reduces transmission failure.     

Loss tolerant video streaming authentication in heterogeneous wireless networks

Multicast video streaming in heterogeneous networks undergoes to very different physical constraints, in fact, such networks are characterized by different QoS parameters, involving one or more transcoding process between the sender and the receivers. Video streaming authentication algorithms must be robust to transcoding processes and must guarantee the copyright of the video owner/producer. We propose a real-time video streaming authentication algorithm that can guarantee the copyright of the video owner and that we prove to be robust to packet loss and transcoding processes.     

引入Foveation视觉模型的MPEG视频码流码率转换

视频码流转换是支持在异质网络环境中进行视频通信的关键技术之一。提出了一种充分利用人类视觉系统特性的MPEG视频码流码率转换方法。与原有方法相比,该方法在转换过程中巧妙地使用Foveation视觉模型,有效地提高转换效率,产生视觉质量更好的低码率码流,并减少了计算量。     

P2P网络移动流媒体转码方法研究

为解决移动设备异构性影响视频流媒体应用的问题,提出了一种P2P网络移动流媒体的交错分布转码方法.该方法允许多个固定节点为一个移动设备转码,生成多个交错子流给目标移动节点,子流在移动节点上组装,降低了转码对固定节点计算能力的需求.分析了节点失效对分布转码造成的影响,交错子流可以减弱这种影响,强化数据包丢失错误恢复机制.比较了该方法与多描述编码之间的性能差异,实验结果表明,应用该方法移动流媒体在节点失效和不良无线信道条件下鲁棒性好.     

Wireless CDN video streaming architecture for IPTV

Wireless IPTV (Internet Protocol TeleVision) aims to make the traditional IPTV and related services available to users anywhere, anytime, on any device, and through any network. Mobile streaming TV is one of the alternatives to deploy such a system; others are DVB-H or MediaFLO. In this paper we propose an alternative CDN-based architecture to distribute contents to different access networks, in order to create a triple screen platform. The core elements of the system are the video streamers, acting as surrogates of the mobile CDN-based architecture, installed in the access networks (including mobile), and the transcoding servers in the premises of the content providers. The paper focused on the wireless part of the system, analyzing the architecture and performance results related with the video coding and the efficiency obtained due to the placement of the streaming servers. The system has been deployed by a Spanish media company for its use with different Telcos, ISPs and media companies.     

Multilayer transcoding with format portability for multicasting of single-layered video

This paper proposes a novel multilayer video transcoding approach for multicasting pre-encoded video to heterogeneous end-systems via diverse grouping of networks. Multilayer transcoding is first addressed by means of multiquality or SNR scalability of the MPEG-2 standard. Frequency domain transcoding and drift-compensated transcoding are derived from the closed-loop and multiloop SNR scalabilities, respectively. The proposed transcoding architectures are verified in terms of eliminating picture drift whilst preserving compatibility with the MPEG-2 SNR decoder. Multilayer transcoding is then addressed by means of multiresolution or spatial scalability of the MPEG-2 standard that supports different video formats. The transcoder retains the full resolution of the incoming video stream in its enhancement layer while generating a low spatio-temporal resolution base-layer compatible with the H.263 video format. Hence providing both multilayer transcoding and video format portability. The resultant video layers are shown to be free from drift with PSNR results comparable to those of the respective scalable encoders.     

Efficient segment-based video transcoding proxy for mobile multimedia services

To support various bandwidth requirements for mobile multimedia services for future heterogeneous mobile environments, such as portable notebooks, personal digital assistants (PDAs), and 3G cellular phones, a transcoding video proxy is usually necessary to provide mobile clients with adapted video streams by not only transcoding videos to meet different needs on demand, but also caching them for later use. Traditional proxy technology is not applicable to a video proxy because it is less cost-effective to cache the complete videos to fit all kinds of clients in the proxy. Since transcoded video objects have inheritance dependency between different bit-rate versions, we can use this property to amortize the retransmission overhead from transcoding other objects cached in the proxy. In this paper, we propose the object relation graph (ORG) to manage the static relationships between video versions and an efficient replacement algorithm to dynamically manage video segments cached in the proxy. Specifically, we formulate a transcoding time constrained profit function to evaluate the profit from caching each version of an object. The profit function considers not only the sum of the costs of caching individual versions of an object, but also the transcoding relationship among these versions. In addition, an effective data structure, cached object relation tree (CORT), is designed to facilitate the management of multiple versions of different objects cached in the transcoding proxy. Experimental results show that the proposed algorithm outperforms companion schemes in terms of the byte-hit ratios and the startup latency.     

A weighted segment-based caching algorithm for video streaming objects over heterogeneous networking environments

Traditional caching technology is not applicable to cache video streaming objects over heterogeneous networking environments. The popularity of mobile devices in the heterogeneous networking environments make the access of Internet content become a common phenomenon. To support different mobile devices in the heterogeneity networking environments, a transcoding proxy is used to transcode different versions of the streaming videos according to clients’ requests. In this paper, we propose a weighted caching replace strategy for video streaming objects over heterogeneous networking environments. A new caching algorithm with static weight transcoding graph and dynamic caching relation tree is introduced. The proposed algorithm is compared with LRU, LFU, CP and PF cache algorithms in three parts: hit ratio, byte hit ratio, and average transmission delay. Experimental results show that the proposed algorithm outperforms than traditional LRU, LFU, CP and PF cache algorithms.     

Complexity of cloud-based transcoding platform for scalable and effective video streaming services

Nowadays, a fast network improves the quality of our daily life and we can enjoy a variety of services over the Internet. Different types of media streaming services have been proposed and utilized as the network speed is now sufficiently fast to deliver high-quality live streaming. Usually, different media streaming services deliver streaming data by using different protocols such as the real-time message protocol (RTMP), real-time streaming protocol (RTSP), and Windows media HTTP streaming protocol (WMSP). In this paper, we propose and implement a cloud-based scalable and cost-effective video streaming transcoding service platform to provide the service of changing real-time streaming protocols (RTMP/RTSP) and codecs (H.263/H.264). A transcoder dispatching problem (TDP) over the cloud platform is also defined, which attempts to serve all the transcoding requests by minimizing the cost of virtual machines. Further, a transcoder dispatching algorithm and an online transcoder dispatching algorithm are proposed for the TDP. These algorithms are implemented on the Amazon EC2 platform. Experimental results demonstrate that by renting different levels of virtual machines dynamically and intelligently, we can provide a scalable and cost-effective transcoding service for bridging heterogeneous streaming media.