Metadata-driven multimedia transcoding for distance learning

Advances in multimedia processing capabilities of electronic devices and the rapid growth of the Internet have contributed to the proliferation of collaborative applications such as distance learning (DL) webcasting. A key technical challenge in such DL systems is providing access to rich media content to any user regardless of device capabilities, network heterogeneity, and personal preferences. A novel MPEG-21-based adaptation architecture is presented to overcome these challenges by performing (1) application layer transcoding that adapts the presentation format of DL content to match device media decoding capabilities and user-desired modality, (2) bitstream transcoding to adapt multimedia to match device processing capabilities and encoding bit-rate supported by the network. Experimental results indicate that the proposed system delivers personalized DL content to meet end-user environmental restrictions with small transcoding overhead. This work is partially supported by the Network for Effective Collaboration Technologies through Advanced Research (NECTAR). The authors would like to thank the Knowledge Media Design Institute (KMDI) at the University of Toronto for use of their resources.     

On designing a shortest-path-based cache replacement in a transcoding proxy

The technology advance in network has accelerated the development of multimedia applications over the wired and wireless communication. To alleviate network congestion and to reduce latency and workload on multimedia servers, the concept of multimedia proxy has been proposed to cache popular contents. Caching the data objects can relieve the bandwidth demand on the external network, and reduce the average time to load a remote data object to local side. Since the effectiveness of a proxy server depends largely on cache replacement policy, various approaches are proposed in recent years. In this paper, we discuss the cache replacement policy in a multimedia transcoding proxy. Unlike the cache replacement for conventional web objects, to replace some elements with others in the cache of a transcoding proxy, we should further consider the transcoding relationship among the cached items. To maintain the transcoding relationship and to perform cache replacement, we propose in this paper the RESP framework (standing for REplacement with Shortest Path). The RESP framework contains two primary components, i.e., procedure MASP (standing for Minimum Aggregate Cost with Shortest Path) and algorithm EBR (standing for Exchange-Based Replacement). Procedure MASP maintains the transcoding relationship using a shortest path table, whereas algorithm EBR performs cache replacement according to an exchanging strategy. The experimental results show that the RESP framework can approximate the optimal cache replacement with much lower execution time for processing user queries.     

集群缓存系统中代理缓存技术的研究

针对集群缓存系统的特点,对其内部各代理缓存进行了详细的研究.在缓存副本的存储方面,采用了面向网站的存储方案,更好的实现个性化服务的功能;在缓存副本的管理方面,采用了将替换和一致性结合在一起的RCA算法,使得整个系统有较高的命中陈旧率;在代理协作方面,通过重定向的方法将请求从未命中的代理转发给缓存了请求的代理,避免了代理之间复制对象,有效地减少了缓存对象的冗余度.通过理论分析推导,证明了它能大大减少访问延迟、有效地减轻了Web服务器的负担.实验证明,本协作方案有较高的命中率.     

DAg-stream: Distributed video adaptation for overlay streaming to heterogeneous devices

Combining the advantages of Peer-to-Peer (P2P) content distribution concept and metadata driven adaptation of videos in compressed domain, in this paper, we propose a simple but scalable design of distributed adaptation and overlay streaming using MPEG-21 gBSD, called DAg-stream. The objective is not only to shift the bandwidth burden to end participating peers, but also to move the computation load for adapting video contents away from dedicated media-streaming/adaptation servers. It is an initiative to merge the adaptation operations and the P2P streaming basics to support the expansion of context-aware mobile P2P systems. DAg-stream organizes mobile and heterogeneous peers into overlays. For each video, a separate overlay is formed. No control message is exchanged among peers for overlay maintenance. We present a combination of infrastructure-centric and application end-point architecture. The infrastructure-centric architecture refers to a tree controller, named DAg-master, which is responsible for tree/overlay administering and maintenance. The application end-point architecture refers to video sharing, streaming and adaptation by the participating resourceful peers. The motivation for this work is based on the experiences and lessons learned so far about developing a video adaptation system for heterogeneous devices. In this article, we present our architecture and some experimental evaluations supporting the design concept for overlay video streaming and online adaptation.

Integrating semantic analysis and scalable video coding for efficient content-based adaptation

Scalable video coding has become a key technology to deploy systems where the adaptation of content to diverse constrained usage environments (such as PDAs, mobile phones and networks) is carried out in a simple and efficient way. Content-based adaptation and summarization are fields that aim for providing improved adaptation to the user, trying to optimize the semantic coverage in the adapted/summarized version. This paper proposes the integration of content analysis with scalable video adaptation paradigm. They must be fitted in such a way that the efficiency of scalable adaptation is not damaged. An integrated framework is proposed for semantic video adaptation, as well as an adaptive skimming scheme that can use the results of semantic analysis. They are described using the MPEG-21 DIA tools to provide the adaptation in a standard framework. Particularly, the case of activity analysis is described to illustrate the integration of semantic analysis in the framework, and its use for online content summarization and adaptation. Overall efficiency is achieved by means of computing activity using compressed domain analysis with several metrics evaluated as measures of activity. Work supported by the Ministerio de Ciencia y Tecnología of the Spanish Government under project TIN2004-07860 (MEDUSA) and by the Comunidad de Madrid under project S-0505-TIC-0223 (PROMULTIDIS).     

From MPEG-7 user interaction tools to hanging basket models: bridging the gap

The content–user gap is the difference between the limited range of content-relevant preferences that may be expressed using the MPEG-7 user interaction tools and the much wider range of metadata that may be represented using the MPEG-7 content tools. One approach for closing this gap is to make the user and content metadata isomorphic by using the existing MPEG-7 content tools to represent user (as well as content) metadata (Agius and Angelides 2006, 2007). Subsequently, user preferences may be specified for all content, without omission. Since there is a wealth of user preference and history metadata within the MPEG-7 user interaction tools that can usefully complement these specific content preferences, in this paper we develop a method by which all user and content metadata may be bridged.

An Effective Cache Replacement Algorithm in Transcoding-Enabled Proxies

In this paper, we address the problem of cache replacement for transcoding proxy caching. Transcoding proxy is a proxy that has the functionality of transcoding a multimedia object into an appropriate format or resolution for each client. We first propose an effective cache replacement algorithm for transcoding proxy. In general, when a new object is to be cached, cache replacement algorithms evict some of the cached objects with the least profit to accommodate the new object. Our algorithm takes into account of the inter-relationships among different versions of the same multimedia object, and selects the versions to replace according to their aggregate profit which usually differs from simple summation of their individual profits as assumed in the existing algorithms. It also considers cache consistency, which is not considered in the existing algorithms. We then present a complexity analysis to show the efficiency of our algorithm. Finally, we give extensive simulation results to compare the performance of our algorithm with some existing algorithms. The results show that our algorithm outperforms others in terms of various performance metrics.     

Media scaling in a multimedia communication system

HeiTS, the Heidelberg Transport System, is a multimedia communication system for real-time delivery of digital audio and video. HeiTS operates on top of guaranteedperformance networks that apply resource reservation techniques. To make HeiTS also work with networks for which no reservation scheme can be realized (for example, Ethernet or existing internetworks), we implement an extension to HeiTS which performs media scaling at the transport level: The media encoding is modified according to the bandwidth available in the underlying networks. Both transparent and nontransparent scaling methods are examined. HeiTS lends itself to implement transparent temporal and spatial scaling of media streams. At the HeiTS interface, functions are provided which report information on the available resource bandwidth to the application so that nontransparent scaling methods may be used, too. Both a continuous and discrete scaling solution for HeiTS are presented. The continuous solution uses feedback messages to adjust the data flow. The discrete solution also exploits the multipoint network connection mechanism of HeiTS. Whereas the first method is more flexible, the second technique is better suited for multicast scenarios. The combination of resource reservation and media scaling seems to be particularly well suited to meet the varying demands of distributed multimedia applications.     

数字媒体适配过程的一般框架、模型及应用研究

丰富的媒体内容和格式、异构的网络以及多样的终端设备,成为通用媒体访问的巨大障碍,媒体适配成为必要.文中分析了MPEG-21数字媒体适配DIA各实体之间的抽象关系,讨论了数字媒体适配的一般框架,建立了基于混合变量的约束优化模型.该模型统一了现有的媒体适配应用研究,能够用一致的算法进行求解.同时,文中从图像理解和视频分析角度,建立了媒体适配的层次结构,对媒体适配应用进行分类,并以当前的主要应用研究如图像适配、视频转码、位率适配、视频对象适配等举例说明.文中也探讨了混合媒体的多模态适配,指出了今后的研究热点和难点,如媒体语义抽取和适配、用户主观测度和媒体访问体验最大化等.