Education In Motion: Streaming

Streaming Media is the action of sending an encoded (digitized) audio and/or video file out across the internet as a series of small data packets that may be viewed by the end user in a real time fashion through the use of a Media Player. The data stream is decoded by a Media Player like the Windows Media Player, Real Media Player, and the Quicktime Player. Essentially the Media Player captures the data packets (stream of packets) and places them in their respective order for real time viewing

The audio and/or video file is streamed by either a Windows Media, Real Networks, or Quicktime Server. These Media servers act as a virtual jukebox that can play a file once, loop a file, or even broadcast a live encode to viewers out across the Internet.

Streaming Media allows the end user to start viewing an audio/video file instantaneously once connected to a media server. Streaming allows for the end user to experience online media in a real time fashion, much like traditional T. V. A download, on the other hand, requires the end user to receive the entire file before viewing or accessing the content. Downloads can potentially take up hours of your time, while streaming allows for immediate viewing.

To digitize audio and/or video you will need to acquire an encoder from Microsoft or Real Networks. Encoders are very easy to use and simply digitize your content into either an .asf,.wmv,.wma(Windows Media) or .rm (Real Networks) file. The current standard encoder software for Real Media is Real Producer 10.

Audio and video are by far the most popular forms of streaming media on the Internet. Most audio and video clips that play in RealOne Player are encoded as RealAudio and RealVideo, although RealOne Player can also play other formats, such as MPEG-1 and MPEG-4 video, as well as MP3 audio.

To create streaming clips, you start with a digitized audio or video file in a standard, uncompressed format. On Windows, WAV (.wav) and AVI (.avi) are the most popular audio and video formats, respectively. On the Macintosh, QuickTime (.mov) and AIFF (.aiff) are commonly used. Unix users often start with MPEG (.mpg, .mpeg).

You can use an audio or video editing program like Adobe Premiere Pro to edit your digitized audio or video file. Using this program, you can set the file length, cropping out any unnecessary parts, for example. Although RealNetworks encoding tools provide some editing functions such as cropping, they do not provide all of the advanced features found in audio and video editing programs, such as tools for sharpening the visual appearance of a video.

Some editing programs can export digitized audio and video directly to streaming formats, such as RealVideo or MPEG-4. Adobe Premiere Pro contains such an encoder. The process for converting original content to Streaming Media is graphically displayed below:

Any computer connected to a network has a connection bandwidth, which is a maximum speed at which it can receive data. Web users with 28.8 Kbps modems, for example, can view only those presentations that stream less than 28.8 Kb of data per second. Presentations that stream more data than that per second may stall because the data cannot get over the modems fast enough to keep the clips flowing. These presentations will not cause problems for users with faster connections, though.

Successfully targeting your audience's connection bandwidth is crucial for producing streaming media. Viewers don't like to wait more than a few seconds for playback to begin after they click a link. And if your clips sputter because they use too much bandwidth, viewers are not likely to stay tuned. Developing a bandwidth strategy helps ensure that clips play back quickly and don't stall. You can also employ methods for delivering good clips to users with slow connections, and great clips to those with fast connections.

Your streaming presentations should never consume all of your audience's connection bandwidth. They must always leave bandwidth for network overhead, error correction, resending lost data, and so on. Otherwise, they may frequently pause while waiting for more data to arrive. The following table recommends maximum streaming speeds for common network connections. To reach 28.8 Kbps modems, for example, a presentation should stream no more than 20 Kb of data per second.

Target Audience	Maximum Streaming Rate
14.4 Kbps modem	10 Kbps
28.8 Kbps modem	20 Kbps
56 Kbps modem	34 Kbps
64 Kbps ISDN	45 Kbps
112 Kbps dual ISDN	80 Kbps
Corporate LAN	150 Kbps
256 Kbps DSL/cable modem	225 Kbps
384 Kbps DSL/cable modem	350 Kbps
512 Kbps DSL/cable modem	450 Kbps
786 Kbps DSL/cable modem	700 Kbps

Helix Producer encodes RealAudio or RealVideo clip for the proper bandwidth (or bandwidths) automatically, based on the audiences you choose. Using SureStream technology, you can encode a single clip for multiple bandwidths. For example, you can encode a single RealAudio music clip for 56 Kbps modems, 112 Kbps dual ISDN, 256 Kbps DSL, and so on. The clip's playback quality improves with each faster speed. When a viewer clicks a link to a SureStream clip, RealOne Player and Helix Universal Server determine which stream to use based on the available bandwidth.

Helix Universal Server and RealOne Player can even adjust the bandwidth choice to compensate for network conditions. If a fast connection becomes bogged down because of high network traffic, Helix Universal Server switches to a lower-bandwidth stream to prevent the presentation from stalling. When the congestion clears, Helix Universal Server switches back to the higher- bandwidth stream. The following illustration shows a SureStream clip streaming to a 56 Kbps modem. It begins streaming at 34 Kbps, downshifts to 20 Kbps during network congestion, then up shifts to 34 Kbps when the congestion clears.

You can choose SureStream and specify many different target audiences when encoding a RealAudio or RealVideo clip with Helix Producer. Note, though, that SureStream does not work when delivering a RealAudio or RealVideo clip with a Web server. If you are using Web server delivery, you can encode each clip for only one target audience. You can choose the Web server delivery option through the Helix Producer user interface when encoding your clips.

An encoder such as Helix Producer typically can turn your source video file into a clip that streams to any target connection. But if the encoder has to squeeze a file down too much to reach a low-bandwidth target, clip quality may degrade. So although the clip will stream well, you might not like the visual results. To ensure high-quality playback, select a video height and width that are appropriate for your target audience. You can set the clip size with your video editing tool. When encoding in the RealVideo format, you can also resize or crop a video when encoding it with Helix Producer.

When streaming larger videos, you get good to excellent quality only at higher connection speeds. Your results will also vary based on the streaming format. RealVideo 9, for example, produces better quality than the RealVideo 8 format. If you plan to stream clips over modems, you can first encode your clip at 320 by 240 pixels to test its quality. If you want better quality, shrink the video dimensions with your editing software, or with Helix Producer during encoding.

Once the audio/video is transposed into Real Media Streaming format the file is placed on a Helix Server. Helix Universal Server is Real Media's preferred host for streaming presentations. It is designed specifically to stream multimedia over networks, Helix Universal Server keeps multiple clips synchronized and uses many advanced features to ensure that clips stream smoothly, even under adverse network conditions.

Each Helix Universal Server has a maximum number of media streams it can send out at once. A Helix Universal Server with a maximum of 500 streams, for example, can stream video to 500 viewers simultaneously.