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Examples of Multimedia Applications

Examples of Multimedia Applications
The internet carries a large variety of exciting multimedia applications. There are three broad classes of multimedia applications: streaming Stored audio/video, streaming live audio/video, and real-time interactive audio/video.

Streaming Stored Audio and Video


In this class of applications, clients request on-demand compressed audio or video files that are stored on servers. Stored audio files might contain audio from a professor’s lecture, rock songs, symphonies, archives of famous radio broadcasts, or archived historical recordings. Stored video files might contain video of a professor’s lecture, full-length movies, prerecorded television shows, documentaries, video archives of historical events, cartoons, or music video clips. This class of applications has three key distinguishing features.

* Stored media. The multimedia content has been prerecorded and is stored at the server. As a result, a user may pause, rewind, fast-forward, or index through the multimedia content. The time from when a client makes such a request until the action manifests itself at the client should be on the order of one to ten seconds for acceptable responsiveness.
* Streaming. In a streaming stored audio/video application, a client typically begins playout of the audio/video a few seconds after it begins receiving the file from the server. This means that the client will be playing out audio/video from one location in the file while it is receiving later parts of the file from the server. This technique, known as streaming, avoids having to download the entire file (and incurring a potentially long delay) before beginning playout. There are many streaming multimedia products, including RealPlayer from RealNetworks [RealNetworks 2004], Apple’s Quicktime [Quicktime 2004], and Microsoft’s Windows Media [Microsoft Media Player 2004].
* Continuous playout. Once playout of the multimedia content begins, it should proceed according to the original timing of the recording. This places critical delay constraints on data delivery. Data must be received from the server in time for its playout at the client. Although stored media applications have continuous playout requirements, their end-to-end delay constraints are nevertheless less stringent than those for live, interactive applications such as Internet telephony and video conferencing.


Streaming Live Audio and Video

This class of applications is similar to traditional broadcast radio and television, except that transmission takes place over the internet. These applications allow a user to receive a live radio or television transmission emitted from any corner of the world. (For example, one of the authors of this book often listens to his favorite Philadelphia radio stations when traveling. The other author regularly listened to live broadcasts of his university’s beloved basketball team while he was living in France for a year.)

Since streaming live audio/video is not stored, a client cannot fast-forward through the media. However, with local storage of received data, other interactive operations, such as pausing and rewinding through live multimedia transmissions are possible in some applications. Live, broadcast-like applications often have many clients who are receiving the same audio/video program. Distribution of live audio/video to many receivers can be efficiently accomplished using the IP multicasting techniques. At the time of this writing, however, live audio/video distribution is more often accomplished through multiple separate unicast streams. As with streaming stored multimedia, continuous playout is required, although the timing constraints are less stringent than for real-time interactive applications. Delays of up to tens of seconds from when the user requests the delivery/playout of a live transmission to when playout begins can be tolerated.

Real-time Interactive Audio and Video

This class of applications allows people to use audio/video to communicate with each other in real-time. Real-time interactive audio over the Internet is often referred to as Internet phone, since, from the user’s perspective, it is similar to the traditional circuit-switched telephone service. Internet phone can potentially provide private branch exchange (PBX), local, and long-distance telephone service at very low cost. It can also facilitate the deployment of new services that are not easily supported by the traditional circuit-switched networks, including Web-phone integration, group real-time communication, directory services, caller filtering, and more. There are hundreds of Internet telephone products currently available [VON 2004]. For example, users of Microsoft’s Instant Messenger can make PC-to-phone and PC-to-PC voice calls. With real-time interactive video, also called video conferencing, individuals communicate visually as well as orally. There are also many real-time interactive video products currently available for the Internet, including Microsoft’s NetMeeting. Note that in real-time interactive audio/video application, a user can speak or move at any time. For a conversation with interaction among multiple speakers, the delay from when a user speaks or moves until the action is manifested at the receiving hosts should be less than a few hundred milliseconds. For voice, delays smaller than 150 milliseconds are not perceived by a human listener, delays between 150 and 400 milliseconds can be acceptable, and delays exceeding 400 milliseconds can result in frustrating, if not completely unintelligible, voice conversations.


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Examples of Multimedia Applications


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