加速比的 PSNR 值减少大多数搜索点这些有非常小的概率当前块最后引用 MMX 技术也被应用于加速各种耗时的计算如绝对差之和(SAD)和 YUV 到 RGB 的转换等。
原来的 H.264 编码器和解码器是使用文件输入和文件输出。
在这个项目中,H264 编码器和解码器是处理文件输入和文件输出。
在这个项目中,H.264 编解码器必须进行修改,使其能为网络摄像头和网络提供必要的接口。
随着 JM 软件用C 实现,它必须在 C 和 C之间建立静态库来保持的编解码速度。
静态库的使用也可以更容易的修改和升级。
下面的图显示了在 4 阶段的改进速度的优化结果。
阶段 1:原始 阶段 2:配置修改 阶段 3:运动 阶段 4:运动技术在压缩和解压缩速度,视频质量也在网络课堂项目的极大关注。
拍摄的图片说明了视频质量 的测试: 原 foreman.qcif 序列(左)和解码序列(右) 原 container.qcif 序列(左)和解码序列(右) 可以从第一个看到第一个图,因为在编码器进行量化,工头的脸模糊。
出于同样的原因,在湖的表面的波变得不明显。
然而,该框架在整体上和他们的质量是可以接受的。
这个项目给予高压缩率仍然是明确的。
4、网络接口 学生可以参加现场讲座通过公共计算机或计算机操作系统比 Windows 更可能发生。
要解决这些问题,开发了一个 Web 界面。
Web 接口包含一个主页,BBS系统,部分音频和部分视频。
网页是由 Dreamweaver MX,Flash MX 开发的。
用户可以找到所有的一般信息的有关项目和文件。
主页 BBS 系统是在互联网上广泛使用的在线讨论。
所有的用户都可以通过发布和回答后互相沟通。
通过提供免费 BBS 系统
源码的 6K 集团,我们使用 ASP 建立了自己的 BBS 系统。
BBS 几种不同的实现可以考虑使用视频和音频部分。
但我们的软件使用特定的视频和音频标准(H. 264,G.723),因此很难用 java 写的匹配的解码器,我们选择了 Windows Media 系列 Windows Media 编码器 9.0 的视频和音频编码器和媒体流可以通过 Windows 媒体播放器轻松解码。
视频播放网页 只有音频 很长一段时间过去了,沟通问题在不同地区和国家之间都受到极大关注,特别是那些在地理上的障碍和距离使得传统的面对面教授是不可能的。
现代技术和互联网已经彻底改变了远程通讯,因此远程学习的概念已经能够实现。
网络课堂提供了很大的灵活性:任何人谁有权访问互联网都可以生活在远程教育中。
教授们可以进行讲座就像在传统的教室,有轻微的变化,利用功能如PRS,白板,视频和音频传输。
结语 和传统的课程交付相比,网络课堂具有几乎无限的班级大小,以及在时间和 “网络课堂”地点上有更大的灵活性。
去年,非典的爆发导致停课。
,学生可以安全的、有效的在家参加讲座,教学调度不需要中断。
今天的因特网是组播的“岛屿”,不能由组播路由器互连。
为了使全球多播组播功能有效,应在一个岛上使用组播功能,岛屿间的单播连接的。
在我们的项目中,我们使用了一个应用层组播框架,称为岛组播(IM),其中组播为两层组织:在上层岛间覆盖建立的同时,IP 组播技术在较低的水平内岛应用。
连同 IP组播可扩展性增加。
这允许一个更大的潜在的学生,因此网络课堂提供传统教学的优势和几乎无限的可供选择的班级规模。
在音频部分,压缩算法 G.723.1 是用来转换成 IP 数据包的演讲。
G.723.1在提供比当前任何 ITU 标准都高的压缩比的前提下,尽管巨大的压缩,仍然保留非常高的声音质量。
在实践中,它几乎不可能在不同 IP 间检测声音的语音质量之间的差异。
我们可以实现延迟小(小于 0.5 秒)并且好的音频质量。
该网络课堂项目实现了 H.264 标准的视频编码和解码。
它提供了更好的视频质量的同时大大减少了视频比特率。
在有限的带宽资源下,给我们一个流畅的视频流。
至于微软的安装,安装使用(MSI)帮助项目提供了一个新的特征,这是不难实现,但很有帮助。
它减少了在编译源和设置软件造成的不必要的误差,同时使我们的产品更加人性化。
为了网络接口,一些技术和软件被使用,如Macromedia Dreamweaver 是为了网页开发;ASP 编程建立的 BBS 系统和 WindowsMedia 编码器 9 系列解码和播放多媒体流。
参考文献 K. -w.cheuk,S. H. Chan 和 J.李;组播岛:IP 组播和应用层组播相结合。
IEEE 国际会议上交流,出现。
pendarakis,Dimitrios,sherlia 石,Dinesh Verma,马塞尔瓦尔德福格尔:ALMI:应用层组播的基础设施,2001 tourapis,亚历克西斯 M.,奥斯卡 C.金,明湖刘:预测运动矢量场自适应搜索技术(PMVFAST)提高基于运动估计块。
附件:外文原文(复印件) Cyberclassroom : A Large-Scale Interactive Distance-Learning Platform Lin,SW1ChengK L2Wang R3Zhou H4 and Chan S H5 1 cs_lswaastu.ust.hk 2 cs_cklaastu.ust.hk 3 cs_wrxstu.ust.hk 4 cs_zhxaastu.ust.hk 5 gchancs.ust.hk Department of Computer Science The Hong Kong University of Science and TechnologyABSTRACTTraditionally lectures are held in classrooms where students are co-located in order tointeract with the instructors. This model is not convenient or cost-effective for somestudents e.g. those who are working have access/mobility difficulties live in remoteareas or experience some social isolation such as during the SARS period.With the pervasive penetration of broadband Internet connections and wirelessmedium Wi-Fi and 3G we have developed a platform so that lectures can beconducted interactively over the Internet. The project termed CyberClassroom offers an experience similar to the traditional classroom today but with the studentsdistributed in the Internet. Students anywhere may raise questions to their instructorsat any time using their PCs or laptops over the Internet and wireless medium. Videoaudio and whiteboard are also streamed to the end-users in real time. The system isscalable to hundreds of students and makes use of current off-the-shelf computingproducts and state-of-the-art networking techniques. It is cost-effective and effectivelybreaks the geographical limitations to attending lectures. Initial feedback from thestudents using the system is positive and encouraging.Key wordsDistance-learning cyberclassroom interactive education distributedsystemmultimedia applications and communication networksINTRODUCTIONWith the tremendous growth in computing devices and computer usage geographicaldistances between people have been significantly reduced. It is easy to name a fewexamples of Internet software that are currently in use: Net Meeting Internettelephony ICQ and so on.Using thesepeople in different pares of the world cancommunicate with each other more economically and efficiently than ever before.Recently the Hong Kong Government has been promoting and putting great effortinto the idea of life-long learning .However working schedules and the pace of lifein Hong Kong make it nearly impossible for people to learm at a fixed time in a fixedplace. In the HKUST Computer Science Department,we have been developing a cyberclassroom platform for interactive distance-learning. This project aims atdelivering live lectures to large groups of students. It allows students to participate incourses from any location at any time from any computer.We show in the following figure the system we developed. It consists of studentsdistributed in the network. The professor may deliver his/her lectures via the Internetwith audiovisual streams and Power Point. He/She may also interact with the studentsthrough polling.There are several unique features and technologies in the project: Network module: We have designed and implemented a delivery mechanism so as to accommodate hundreds to thousands of students without the need for powerful servers and clients. Our network protocol has been presented in major conferences and seminars and has received wide interest. Audio module: The audio has to be delivered to the students in good quality. We have used a highly compressed audio which does not take up much network bandwidth. The encoding standard we use is called G.723. Video module: We have implemented the most recent encoding technology H.264 for video compression. It guarantees good quality of video while greatly minimizing the use of network and system resources. As a result bandwidth requirement for this software is greatly reduced. Web interface: The focus of this part is to support a web interface. With this feature students can have lessons anywhere they can find a computer with access to the web. To further increase user-friendliness the CyberClassroom project also provides installation files. Simple mouse clicks according to the guidelines make installation much more convenient. No compilation or linking as required in last years project is necessary.In the following we explain the modules in detail.NETWORK MODULESince the Cyberclassroom is a real-time application and the number of peopleattending a class is usually quite large a stable and scalable network layer isimportant. The main function of the network is to distribute the lecture materialsnamely video and audio to all students attending the lecture. This technique is calledmulticasting.Traditionally there are two ways of multicasting. Application Layer MulticastALMand IP-multicast. In ALM the multicast is done by a sequence of unicasts along alogical tree of nodes/users. It is used to solve the adaptability problem ofIP-multicasting. Since the transmission of the data to a group of ALM hosts is done byunicast protocols such as TCP and UDP it is supported by any router on the Internet.However as all data transmissions are done by unicast redundant transmission whichresults in inefficient use of bandwidth would be the major problem in using ALM. Incontrast by using the IP multicast technology data only needs to be transmitted onceand every host within the same group receive it. Compared with multiple unicastcommunication IP multicast is more efficient as eliminating redundant transmissionsaves bandwidth. To utilize the power of both ALM technology and the IP-multicasttechnologywe therefore designed and implemented a .
上一篇:
基于书签的校园搜索引擎【精品
下一篇:
大学生汉语写作水平与英语水平相关性研究