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    Streaming media.doc Streaming media.doc Document Transcript

    • Streaming media Hong Chun The problem we face With the popularization of Internet, the demand of audio and video signals transmission is increasing. After the broadcasting and TV show were put on online, (which are tremendous huge, although we’ve got Data Compression), the waiting time for the transmission of a video become a headache since you have to wait for 40min or longer when your bandwidth has a limitation. This is not only time costing and hard disk room demanding; also can not satisfy the consumers’ needs. The appearance of steaming media, has improved this situation in a certain extent. What is streaming media? Streaming media technology originated in the narrowband Internet period. Due to the needs of economic development, people eagerly need a network technology for long- distance communication of information. Since a company called net works progressive was first established in the United States in 1994, streaming Media began to appear on the Internet officially. In 1995, they launched a audio receiving system called ”real audio”, and lead the turbulent flow of streaming technology trends in the next few years. In September 1997, the company changed its name to Realnetworks, which would be involved later in this paper. But then, Apple and Microsoft saw the excellent prospects of streaming media, with their powerful offensive competition, Realnetworks felt the existing crisis. On the other hand, they had promoted the rapid development of the streaming media and streaming media to make an astonishing speed which enjoys a popular support among users. The definitions of streaming media are various and you may confuse about them. One statement by Wolfgang Effelsberg and Ralf Steinmetz is: Streaming media refers to media types with time constraints and a continuous data flow, mainly video and audio transmission. Usually, streaming media technology has three main characteristics: 1. it enables real-time or on-demand access to audio, video, and multimedia content through the Internet. More specifically, media is stored and published on the Web in streaming formats can be made available for access at any time. 2. Streaming media is transmitted by a media server application, and is processed and played back by a client player application, as it is received. Users can start playing back streaming media as soon as enough data has been received—without having to wait for the entire file to have arrived. As data is transferred, it is temporarily stored in a buffer until enough data has accumulated to be properly assembled into the next sequence of the media stream. 3. A streamed file is received, processed, and played simultaneously and immediately, leaving behind. An important advantage of streaming media technology is the copyright protection it provides. No copy of the content is left on the receiving device. Therefore, the recipient can neither alter nor redistribute the content in an unauthorized manner. By streaming media technology, the streaming transmission can be realized, which means the audio, video or animation are transmitted continuously and uninterruptedly. Users do not need to download the entire files, just a few seconds delay (or several minutes which depends how horrible your internet and computer are...), you can enjoy the movies or music. When they are played in your computer, the rest of the files will continue to be downloaded from the server. In early times streaming media was mainly applied in the narrowband Internet, which was limited by bandwidth conditions. Until1999, people can only see a small video broadcast window on the Internet. In the second half of 2000, within the scope of the Internet as a global warming, the broadband IP network is no longer a dream. As
    • streaming media technology advocates and sponsors in America, RealNetworks, Microsoft, and Apple announced to the world that they had the latest streaming media technology solutions in broadband at almost the same time. We can see that in a short period of time, streaming media technology was developing rapidly. Traditional download, progressive download and streaming Traditional download - People are used to downloading the numerous media from the Internet. But when you are in a narrowband world, it is very inconvenient to download a large amount of media files. You have to wait 8 hours or more to download a movie or in some case, the download does suddenly not work. Even you might spend a lot of time downloading media files, only to find that when you play them, they are not what you really wanted or expected. Until recently, audio and video on the Web was primarily a download-and-play technology. You had to first download an entire media file before it could play. It was like pouring milk into a glass and then drinking it. But because media files are usually very large and take a long time to download, the only content found on the Web was short 30- second clips—often even shorter. Even these files could take 20 minutes or longer to download. In other words, it took a long time to pour the milk, and then it would barely quench your thirst…this passage is from Microsoft Windows Technologies Web Site which clearly spelled out the shortage of traditional download. Progressive download – it is also called pseudo-streaming. It allows playback to begin before the file is completely downloaded and it also allows playback of content that has been received to continue, while the remainder is still being downloaded. By progressive download users can view the beginning of the media, as the remainder is being downloaded, and to quit the download if the content is not what the users want. Progressive download allows audiences to see and hear the content immediately—as it is being downloaded—but only when the download speed can be maintained at the needed rate. If the download slows down because of the Internet connection, causing the audio and video playback may not always stay synchronized, playback may always stay a halt, as the player waits for the download to catch up. Nevertheless, progressive download has to write the media file to disk, using the memory of the receiving device. Streaming media – unlike other form of downloadable media files, streaming media is using a new Web transfer protocols. Streaming media files are usually encoded in several versions, optimized for different data rates. The server can even intellectively select the best version, based on information brought back from the client regarding the platform and the connection speed. If the connection slows down, the streaming media can be adjusted, depending on the media server and client player software. You can easily get benefits using a specialized streaming media server, like efficient use of the network bandwidth, better audio and video quality, support for large numbers of users, and content copyright protection. How does streaming media work? Although the principle of streaming media seems to be complex, it is usually based on the following steps: 1.The user selects a media file, causing a request to be sent to the Web server. 2. The Web server relays the request to the media server. 3. The Media server streams the media file back to the user’s computer. 4 The client decodes and plays back the media file. Network Protocol supporting streaming media 1 . RTP The Real-time Transport Protocol (or RTP) is an Internet protocol standard that specifies a way for programs to manage the real-time transmission of multimedia data over
    • either multicast network services. It provides end-to-end delivery services for data (such as interactive audio and video) with real-time characteristics. RTP is commonly used in Internet telephony application and provides the wherewithal to manage the data as it arrives to best effect. RTP components include: a sequence number, which is used to detect lost packets; payload identification, which describes the specific media encoding so that it can be changed if it has to adapt to a variation in bandwidth; frame indication, which marks the beginning and end of each frame; source identification, which identifies the originator of the frame; and intramedia synchronization, which uses timestamps to detect different delay jitter within a single stream and compensate for it. RTP combines its data transport with a control protocol (RTCP), which makes it possible to monitor data delivery for large multicast networks. Monitoring allows the receiver to detect if there is any packet loss and to compensate for any delay jitter. Both protocols work independently of the underlying Transport layer and Network layer protocols. Information in the RTP header tells the receiver how to reconstruct the data and describes how the codec bit streams are packetized. 2. RTCP RTP Control Protocol (RTCP) is a sister protocol of the Real-time Transport Protocol (RTP). It is defined in RFC 3550. RTCP stands for Real-time Transport Control Protocol, provides out-of-band control information for an RTP flow. It partners RTP in the delivery and packaging of multimedia data, but does not transport any data itself. It is used periodically to transmit control packets to participants in a streaming multimedia session. The primary function of RTCP is to provide feedback on the quality of service being provided by RTP. RTCP components include: quality of service (QoS) feedback, which includes the numbers of lost packets, round-trip time, and jitter, so that the sources can adjust their data rates accordingly; session control, which uses the RTCP BYE packet to allow participants to indicate that they are leaving a session; identification, which includes a participant's name, e-mail address, and telephone number for the information of other participants; and intermedia synchronization, which enables the synchronization of separately transmitted audio and video streams. 3. RTSP Real Time Streaming Protocol (RTSP) was proposed by Netscape and RealNetworks jointly. This protocol defines how to deliver media data effectively by one-to-many applications through IP networks. The structure of RTSP is based on RTP and RTCP. It uses RTP or TCP to complete the data transmission. Compared with HTTP, HTTP transmits HTML, RTSP transmits media data. The request of HTTP is sent by the client, and the server responses; For RTSP, client and server can both send a request which means the RTSP is a two-way protocol. Real-Time Streaming Protocol establishes and controls one or several streaming media of consecutive time synchronization. Despite the possibility of cross of the continuous media streaming and control streaming, usually it does not send continuous streaming itself. In other words, RTSP serves as the remote control of network multimedia. RTSP does not bind with the transmission layer, such as TCP. When RTSP is in connection, RTSP server users can open or close a number of reliable transmission connections as to send a RTSP request. In addition, the user can use connectionless transport protocol, such as UDP. Some RTSP servers use RTP as the transport protocol for the actual audio/video data. Many RTSP servers use RealNetworks's proprietary RDT as the transport protocol. 4. RSVP The Resource Reservation Protocol (RSVP) is a network layer protocol designed to reserve resources across a network for an integrated services Internet. RSVP does not
    • transport application data but is rather an Internet control protocol, like ICMP, IGMP, or routing protocols. RSVP provides receiver-initiated setup of resource reservations for multicast or unicast data flows with scaling and robustness. RSVP can be used by either hosts or routers to request or deliver specific levels of quality of service (QoS) for application data streams or flows. RSVP defines how applications place reservations and how they can relinquish the reserved resources once the need for them has ended. RSVP operation will generally result in resources being reserved in each node along a path. Because audio and video data streaming is more sensitive than traditional data in the aspects of networks delay, the transmission of high-quality audio and video needs much more other conditions in addition to the bandwidth requirements. RSVP is developed by the Internet Resource Reservation Protocol. Using RSVP, part of the use of network resources (bandwidth) can be set aside, which can provide QoS in the transmission of streaming media in a certain extent. RSVP is not itself a routing protocol and was designed to interoperate with current and future routing protocols. It is worth noting that RSVP by itself is rarely deployed in telecommunications networks today [citation needed]. However, the traffic engineering extension of RSVP, or RSVP-TE, is becoming more widely accepted nowadays in many QoS-oriented networks. Streaming media architectures and their products An architecture is an interdependent system comprised a variety of components that all work together to perform certain functions. Streaming media architectures are comprised of encoding and transmission methods, server software, and players. Currently, the three most popular streaming media architectures are RealMedia, Windows Media, and QuickTime. The streaming market is dominated by these three architectures. RealMedia RealNetworks is a provider of Internet media delivery software and services based in Seattle, United States. The company has three best known creations: RealAudio, a compressed audio format which has nearly the quality of CD sound; Real Video, a compressed video format which transforms uninterrupted video data; RealFlash, a recently high compression animation format, which was developed with the joint of Macromedia. It makes Real system deliver the high-quality multimedia by various networks. RealMedia audio streaming files can contain RealAudio and Real Video streams, and several other formats like SMIL. RealNetworks produced the RealPlayer streaming media software remains in the market place. After all, it has a long history of being in the streaming media market with a large number of users. March 5, 2002. RealNetworks released the final version of the RealOne (Gold version). Windows Media Windows Media is a multimedia framework for media creation and distribution for Microsoft Windows. It consists of a software development kit with several application programming interfaces and a number of prebuilt technologies. The product Windows Media Player (WMP) is a digital media player and media library application that is used for playing audio, video and images on personal computers running the Microsoft Windows operating system, as well as on Pocket PC and Windows Mobile-based devices. The suffix of files is .wmv and .asf. The ASF (Advanced Stream Format) is the core of Windows Media. Microsoft ASF is defined as the simultaneous media containers unified format. ASF is a data, audio, video, images and other multimedia information format through the control of orders script and realized the transmission of streaming media content in the form of data packets to the network. ASF’s greatest advantage is small in size and therefore suitable for network transmission. Using Microsoft Windows Media Player, this format can be played directly. Users can make graphics, sound and animation into one ASF format data. Other formats of video and audio can also be converted to in ASF format. Moreover, users can also use
    • sound card and video capture cards, such as a microphone to maintain data recorders so as to save an ASF format. In addition to being a media player, Windows Media Player includes the ability to rip music from, and copy music to compact discs, synchronize content with a digital audio player (MP3 player) or other mobile devices, and let users purchase or rent music from a number of online music stores. QuickTime QuickTime is a multimedia framework developed by Apple Inc., capable of handling various formats of digital video, media clips, sound, text, animation, music, and several types of interactive panoramic images. Apple QuickTime is the first video industry standards. After the release of version 4.0 of QuickTime in 1999, it began to support for real-time broadcast. Everyone is very satisfied with QuickTime 5.0 with all aspects of functional which is simple and intuitive and this is its greatest strength. The later version of Apple QuickTime has upgraded the quality of image. The suffix of files is .mov. Unfortunately, the three parallel standards are not compatible with each other. This means that each major network required a different device so as to translate the signal into video and audio. That means, the RealMedia server cannot stream Windows Media and QuickTime files; the Windows Media server cannot stream QuickTime and RealMedia files; and the QuickTime server cannot stream RealMedia and Windows Media files. For example, each home would have needed an ABC television set, a CBS television set, and an NBC television set, if the household wanted to watch programs on every channel. Each of architecture has pro and cons. Although these three architectures look similar, in different situation you should use different one. Your project, your audience, your objectives, and other factors are all to be considered. Effect and influence of streaming media With the rapid development of the information society, media streaming media technology has played a leading role on the Internet, which includes video-on-demand; distance education, video conference, advertising network and Internet broadcast news. The unprecedented application has made it easy for people to get the world of information and make emotional exchanges. It is generally optimistic about the future development of streaming media technology. Streaming media has become the mainstream of the Internet applications and its extensive and unique charm has captured the Internet market so as to promote innovation and stimulate the development of the information economy. From today's perspective, streaming media effect and influence is very positive and encouraging. Reference:  Adobe Dynamic Media Group (2001) A Streaming Media Primer  Dale Sorenson (2001) MacInTouch Special Report: Streaming Media Market Report – 2001 http://macintouch.com/stream2001.html#companies  Real-Time Transport Protocol (2002) http://searchnetworking.techtarget.com/sDefinition/0,,sid7_gci812019,00.html  Real Time Streaming Protocol http://en.wikipedia.org/wiki/RTSP  What is Streaming Media and how does it work? http://service.real.com/help/player/plus_manual.g2/htmfiles/whatisrp.htm  Resource reservation protocol http://en.wikipedia.org/wiki/Resource_Reservation_Protocol