Prior to the introduction of streaming media. a media file would have to be completely downloaded to a user's machine before it could be played. Using "downloadable" media meant that the user would have to wait to hear or see the material they requested. Depending  on the speed of the user's connection and the length of the audio or video clip, this wait could be as long as an hour. MP3 music files are examples of downloadable media.

     With  the introduction  of  RealAudio  in  1995, Real­ Networks pioneered a new approach to significantly reduce the wait time required to begin playing media files. Streaming media allows the simultaneous download and playback of audio and video. When a user requests a streaming media file (usually by clicking on a link on a web page). several things happen. First, the user's computer launches a streaming media player. The two leading streaming media players are RealOnePlayer by RealNetworks and Windows Media Player by Microsoft. Basic versions of both players are free·downloads. In the next stage, the streaming media player begins downloading the media file. When a certain amount of the file (usually 30 seconds) has been downloaded, the media player begins to play back the file. As long as the media file downloads faster than  it plays, the user experiences uninterrupted audio and video.

     In order to deliver video and audio via the Internet, streaming media has had to address two challenges: file size and variable bandwidth. Compared to the text and graphics that comprised the majority of early Internet content, audio and video files are huge. To distribute audio and video. file sizes must be significantly reduced. Streaming media uses three approaches to reduce the size of media files: compression, frame rate reduction, and image size reduction.

     Compression techniques reduce redundant and marginally valuable information from media files to reduce their size. One of the most common compression techniques used by streaming media is frame differencing. In compressing streaming media files, the video material is analyzed to determine which visual elements (or pixels) change from one frame to the next. In transmitting the streaming file, only those elements that change are transmitted. In this way, the amount of information that has to be downloaded is significantly reduced.

     The physical dimensions of video are reduced to reduce file size. Whereas the typical computer screen displays at 640 by 480 pixels. streaming media video sizes are usually 240 by 180 pixels. This smaller video image translates into a smaller file size for streaming media content.

     The final way in which the file size for streaming media video files is reduced is by reducing  the number of video frames displayed per second. Typical television video is displayed at 30 frames per second to achieve  the  perception  of  motion.  Streaming   video files reduce the frame rate to around 15 frames per second. This reduced frame rate still produces fluid motion but with much-reduced file sizes.

     The second challenge facing streaming media is variable bandwidth. Network congestion causes the speed at which data is transmitted via the Internet (throughput) to vary widely. For the user to experience uninterrupted audio and video, there must be a method to level out the peaks and valleys in transmission speeds. Streaming media uses a ·'buffer" to guarantee consistent playback. The streaming  media player downloads a reserve of audio and video information into the buffer before it begins to play. Then the player releases a steady flow of data from the buffer for playback. The buffer absorbs the fluctuations in transmission speeds to  guarantee  constant and interrupted playback. Should the buffer "drain" during playback, the video will stop to allow the buffer to be refilled. This "rebuffering" is common with slower connection speeds and in times of heavy network traffic.

     At present, streaming media does not threaten the dominance of broadcast television. The amount of processing power required on the receiving end necessitates that streaming media be played on a computer, and few viewers are willing to replace their television set with a computer . But streaming media does hold promise in certain niche markets. Sports have been an important application for streaming media because it allows fans living out of a given television market to follow their favorite teams. Streaming media also plays an important role in distance education by offering audio and video of lectures. Streaming media has been prevalent in the online distribution of adult entertainment/pornography materials. High levels of viewer motivation encourage users to tolerate the special limitations of streaming media to experience content that is important to them.

     In its early days, most streaming media was available for free. However, new business models have evolved, and subscription is playing an increasing role in online media. Major League Baseball (MLB). the National Basketball Association (NBA). and the National Association for Stock Car Auto Racing (NASCAR) have all developed "pay for play" offerings that allow viewers to pay a single monthly subscription to access all events. And MLB has even developed a new product called "Custom Cuts," which offers edited games that can be viewed in much less time.

     Increasingly, streaming media is being used to complement existing television programming. Networks are using streaming media to distribute portions of their programming such as promos and highlights. However, video producers are discovering that the special nature of streaming media requires different production approaches. The small screen size in streaming media presentations favors close-ups. Reduced frame rates affect screen transitions, such as dissolves. And compression techniques can significantly impact the playback of pans and handheld shots. Video producers are now becoming more adept at selecting only certain types of scenes to be distributed via streaming video or are shooting special video for streaming distribution.

     Currently, there is a large and growing number of streaming media users. RealNetworks reports that it currently has over 300 million unique users of its streaming media players. As broadband connectivity proliferates, there is every reason to believe that streaming media will continue to grow.