The hottest streaming media technology and its app

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Streaming media technology and its application in broadband networks

in the construction of broadband networks, people gradually realize that broadband applications are the source of strength that really supports the development of broadband networks, and also the source of benefits for broadband network operators. Streamingmedia technology based on medium and high-speed networks was born. Its birth and development promoted the innovation of the overall architecture of the Internet, and gave broadband applications more entertainment and interactivity. At present, in China's broadband network market, MPEG-1, MPEG-2, real, WMT, QuickTime and other streaming media products based on different compression and coding methods have become the darling of broadband network and have attracted increasing attention

I. concept and characteristics of streaming media

streaming media refers to a format of continuous audio/video data transmitted and played in chronological order on the data network by using variable bandwidth technology. Streaming media only caches part of the content before playing, and does not download the whole file. At the same time of data streaming, users can use the corresponding player or other hardware and software to press on the computer, so as to avoid forming bubbles in the components. Streaming multimedia files such as animation, video and audio can be decompressed and played, which saves download waiting time and storage space, and greatly reduces the delay, The rest of the multimedia files will continue to be downloaded in the server in the background

streaming media data stream has three characteristics: continuity, real-time and timing, and has a strict pre and post timing relationship

II. Streaming media system and its key technologies

1 The composition of the streaming media system

the streaming media system includes five parts: the encoding/decoding, storage, streaming media server, media transmission network, and user-side player of the audio/video source. The original audio/video stream is encoded and compressed to form a media file storage, and the media server transmits the media file to the user-side media player according to the user's request

2. Streaming media file format

streaming media file is to transmit a material (animation, video, etc.) in sections. Users do not have to wait for the entire content to be transmitted, they can watch real-time and continuous content, and even pause, fast forward, and fast reverse at any time. Due to the different file formats developed by different companies, the transmission methods are also different. The following are several popular streaming media file formats

(1) RealNetworks RM video image format and RA's audio format

realsystem of RealNetworks is composed of media content production tool realproducer, server-side RealServer, and client software. Its streaming media files include RealAudio, realvideo, realpresentation, and realflash. SureStream technology used in RealAudio and realvideo is a representative technology of RealNetworks, which can automatically and continuously adjust the flow of data stream to meet various network bandwidth requirements in practical applications, and easily realize the playback of video, audio and 3D animation on. Real format has extremely high compression ratio and good transmission capacity. Its streaming file is produced by realproducer software, which changes the source file or real-time input into a streaming file, and then transmits the streaming file to the server for user demand

the server-side software is realserver8, which has network management function and supports a wide range of media formats and streaming media business models. RealPlayer, a client player, has more than 160million registrations worldwide, accounting for 60% of the online video streaming on demand market

due to its mature and stable technical performance, companies such as Internet giant America (AOL), ABC, at&t, Sony and timelife and major radio stations on the world use realsystem to transmit real-time audio and video media information and real-time music broadcasts to all parts of the world. In China, a large number of film and television, music on demand and live broadcasts of the Spring Festival Gala and the opening ceremony of the Kunming WorldExpo have adopted the realsystem system

(2) Microsoft ASF format

Microsoft has also launched a complete set of information streaming playback scheme microsoftmediatechnology, including streaming media production (medi nearly 21% of enterprise losses atools), publishing (MediaServer) and playback software (me? Diaplayer). Mediatools provides a series of tools to help users generate ASF format multimedia streams (including real-time generated multimedia streams), which is an important part of the whole scheme. It is divided into creation tools and tools. Creation tools are mainly used to generate ASF format multimedia streams, including mediaencoder, author, vidtoasf, wavtoasf, presenter five tools; The tools mainly manage the multimedia stream information in ASF format, including post production tools asfindexer and asfchop, as well as asfcheck, which checks the ASF stream and corrects errors. ASF is a data format including audio, video, image, control commands, scripts and other multimedia information. It is transmitted on the Internet by dividing into network packets to realize streaming multimedia content publishing. ASF supports any compression/decompression coding mode, and can use any underlying network transmission protocol, which has great flexibility. MediaServer can ensure the confidentiality of files, prevent them from being downloaded, and enable each user to browse the page with the best movie quality. It has a variety of file publishing forms and monitoring and management functions. Mediaplayer provides powerful streaming information playback function, which can be used not only for web playback, but also for playing video files outside the browser

Microsoft bundled microsoftmedia technology with win? In dows2000, it is convenient, advanced, integrated and low-cost. In addition, ASF will also be used as the standard file format for multimedia content in the Windows version, which will undoubtedly have a significant impact on the application and development of the Internet, especially streaming technology. However, there is still a gap between the overall solution and RealNetworks software, and it can only be used on the Microsoft platform

(3) apple QuickTime

Apple began to release QuickTime in 1991. It supports almost all mainstream personal computing platforms and various formats of still image files, video and animation formats. It is an important foundation for creating 3D animation, real-time effects, virtual reality, a/V and other digital streaming media

quicktime includes server quicktimestreamingserver, player quicktimeplayer with functions (free), production tool quicktime4pro, image browser pictureviewer, and QuickTime plug-in that enables Internet browsers to play QuickTime movies. Quicktime4 supports two types of streams: real-time streams and quick start streams

quick using real-time streaming? - time movies must be played from servers that support QuickTime streaming. They are streaming media in the true sense, and use real-time transfer protocol (RTP) to transmit data. Quick start movies can be played from any webserver, using hypertext transfer protocol (HTTP) or file transfer protocol (FTP) to transfer data

at present, fox, Fox Sports, bbcworld, weatherchannel and other institutions have joined the ranks of QuickTime content providers, using QuickTime technology to produce live broadcast programs. Many new movie clips retrieved through Hollywood studios () are also stored in QuickTime format

(4) other

in addition to the above three main formats, streaming media technology in multimedia courseware and animation includes Macromedia's shockwave technology and metastream technology of meatacreation company

through Macromedia's shockwave technology, you can easily add images, animations, interactive interfaces and other operations to web pages. Shockwave is closely linked with Macromedia products, including flash, shockwave forauthorware, shockwave fordirector and other technologies

metastream3d's graphics design software is raydreamstudio5 and raydream3d, which can easily create, publish and browse scaled 3D graphics on. It has the characteristics of small file volume and streaming transmission, and has a higher compression rate than any other existing internet3d technology. It is mainly used in game developers, page designers, e-commerce, scientific researchers, professional designers, etc

in addition, MPEG-4 is considered to be a technology against Microsoft's entry into the media market. MPEG-4 compresses large digital files into smaller files for transmission on the Internet, and provides interactive functions, so that film and television programs have the interactivity that only Internet stations and video games can provide today

3. The key technology of streaming media system

in streaming media system, the three most critical factors that affect the playback quality of streaming media are: the performance and efficiency of coding and compression, the nature of media server, the large range of assets of foreign companies, and the quality control of media streaming transmission

(1) encoding/compression

encoding in streaming media system is used to create, capture and multimedia data to form streaming media format

there are many factors that affect the coding performance of audio/video streams: the first is the coding efficiency, which requires that the bitrate of media streams should be as low as possible on the premise of ensuring a certain audio/video quality, so as to achieve the purpose of compressing streaming media files. The second is the redundancy and reliability of coding. Unlike ordinary multimedia file compression/coding, streaming media files need to be transmitted in real time on the network, so the impact of data loss in transmission on decoding quality must be considered. In the Internet environment, the most typical method is multiple description coding (MDC). MDC compresses the original video sequence into multi bit streams. Each stream corresponds to a description, which can provide acceptable visual quality. The combination of multiple descriptions provides better quality. Finally, we need to consider the ability of rate adjustment. One method is to use scalable hierarchical coding to generate multiple substreams. One of the bitstreams is the basic bitstream, which can decode independently and output rough quality video sequences. Other bitstreams play the role of quality enhancement, and all the bitstreams together restore the best quality video sequences. When the network rate changes, the rate of the code stream can be controlled by adjusting the level of the stream output, so as to adapt to the change of the network rate

(2) media server

the media server in the streaming media system is used to store and control the data of streaming media

with the expansion of streaming media scale, the performance of streaming media server has become an important factor restricting the expansion ability of streaming media services. The key performance indicators of streaming media server are the streaming output capacity and the number of concurrent requests that can be supported at the same time. There are many factors that affect the performance of streaming media server, including CPU capacity, i/o bus, storage bandwidth and so on. Usually, the concurrency number of a single streaming media server is less than a few hundred. Therefore, in order to have better performance, the current high-performance streaming media server adopts the structure of large-scale parallel processing, such as the structure of hypercube to connect each streaming media service unit. Another method is to use a simple PC cluster. In this way, multiple PC streaming media servers are connected locally, and the front end uses content exchange/load balancer to distribute streaming media service requests to each PC media service unit. The performance of the latter method is not as good as that of the former method, but the cost is low and easy to implement

(3) streaming media transmission network

streaming media transmission network is suitable for multimedia transmission protocol and even real-time transmission protocol

streaming media transmission on Internet

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