通信与电子信息工程专业英语 课文翻译 聂敏著第7单元TEXT_AB.pptVIP

Unit 7 Digital Compression Technologies;Unit 7 Video and Audio Compression;Many communication systems that have become commonplace in the past few years depend on compression technology. For example, digital mobile telephones use compression to increase the number of users who can be served and to increase the battery life of mobile handsets. Digital TV and HDTV delivery to homes would be impossible without compression to fit content into consumer delivery systems. ;Digital cameras use data compression to fit more pictures into a fixed amount of storage. MP3 players and Apple iPods use compression to take files from audio CDs and make them small enough to fit into the memory of a portable player. ;Compression allows a 2-hour movie to fit onto a 4-inch DVD in place of an 812-foot long (248-m) VHS tape. Satellite television uses compression to allow hundreds of video channels to be distributed economically to viewers.An understanding of video and audio compression is essential to understanding and using modern video transport systems, including video over IP networks. VHS：video home system 家用录放机 VOIP:video over Internet Protocol 网络电视 ;Compression technology is a continuing field of research. As better mechanisms are developed, more information can be carried in fewer and fewer bits. Plus, as processing power increases, these techniques can be implemented on ever-faster, ever-cheaper processors. So compression is constantly being used in more and more applications. In this section, well look at the reasons for using compression as well as its benefits and drawbacks.;The input of compression systems can be a computer file, such as a document, an image, and/or a video/audio recording. Or the input can be a continuous stream of data, such as a digital video or audio signal. Either way this information is fed into the compression engine.;The output of the compression engine is a second data file or data stream that contains fewer bits than the input file or stream. This