If you're new to media streaming, this chapter provides background on media production, and introduces you to important streaming concepts. Although it doesn't cover the steps required to encode streaming clips, it tells you where to find the necessary tools and documentation to do so.
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For More Information: See also Appendix A, which provides quick answers to common questions about media production and streaming. |
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).
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Tip: If RealOne Player can open a clip, you typically can stream that type of clip with Helix Universal Server. Only compressed clips stream well, though. Uncompressed AVI is not a good streaming format, for example, because it requires a lot of bandwidth for even a small clip. |
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Note: Although RealOne Player can play proprietary formats used by other media players, such as Windows Media and QuickTime, it does not support the use of a Ram file or SMIL with these formats. When streaming one of these formats to RealOne Player, you must author presentations using the markup conventions supported by Windows Media Player or QuickTime Player, respectively. |
You can use the audio or video editing program of your choice 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.
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Tip: The quality of a streaming audio or video clip starts with the source file. The more you know about audio and video editing, the better you'll be able to produce a great streaming clip. For some pointers about preparing files for encoding, see the audio chapter and video chapter of the RealNetworks Production Guide. |
Some editing programs can export digitized audio and video directly to your streaming formats, such as RealVideo or MPEG-4. If your editing program cannot export clips, or you don't want to use this feature, you can use an encoding tool to encode clips from files in standard formats. Helix Producer Basic is a free tool for encoding RealAudio and RealVideo clips. Helix Producer Plus is an enhanced version that offers more encoding features.
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For More Information: You can get more information about Helix Producer, as well as download this tool from http://www.realnetworks.com/products/producer/index.h tml. |
Although audio and video command the biggest share of streaming media on the Web, they are not the only types of clips that you can stream. RealOne Player can plays many different types of clips, giving you a lot of ways to combine diverse media into a single presentation. The following sections explain the types of clips in addition to audio and video that can play in the RealOne Player media playback pane.
With Macromedia Flash animation, you can build anything from streaming
cartoons to e-commerce applications. Using version 5 of the Flash application,
you can export an animation directly for streaming to RealOne Player,
complete with a RealAudio soundtrack. A streaming Flash clip uses the file
extension .swf. Learn more about Flash from Macromedia's Web site at:
http://www.macromedia.com/software/flash/
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Tip: A Flash chapter in RealNetworks Production Guide explains how to optimize a Flash clip for streaming, as well as how to encode URLs into the clip. |
Still images in the GIF, JPEG, or PNG format can display in the media playback pane, as well as in the media browser and related info panes. Using SMIL, you can create streaming presentations that include images along with audio or video clips. You can even turn the images into interactive buttons. Chapter 8 explains the basics of how to play multiple clips in the media playback pane.
When you want to create a streaming slideshow, the easiest solution is to use RealSlideshow™ or RealSlideshow Plus. These tools have drag-and-drop interfaces that let you quickly build your slideshow, which can include text captions, audio narrations, and background music. Get RealSlideshow at:
http://www.realnetworks.com/products/index.html
Streaming slideshows are based on the RealPix markup language. Instead of
using RealSlideshow, you can write your own markup to assemble images into
a RealPix presentation that has eye-catching special effects such as dissolves
and zooms. A RealPix markup file uses the file extension .rp. Learn the RealPix markup language from RealNetworks
Production Guide, available for download from the following Web page:
http://service.real.com/help/library/encoders.html
To create streaming, timed text, you can use RealText, a simple markup
language that lets you subtitle videos, for example, or create hypertext links
within the media playback pane. A RealText markup file uses the file
extension .rt. The RealText chapter of RealNetworks Production Guide
explains how to write this markup.
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.
For any other connection speed, calculate the maximum streaming speed as:
Helix Producer encodes your 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 upshifts 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.
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Tip: You can also use SMIL to stream different presentations based on viewer bandwidth. After you learn the basics of SMIL in this guide, refer to the switching chapter of RealNetworks Production Guide. |
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.
The following table lists four common video clip dimensions that maintain the 4:3 aspect ratio used in television. For each clip size, the table indicates the general playback quality you'll get when streaming a video clip to various target audiences. "Excellent" video quality means few visual imperfections and a video frame rate that results in acceptably smooth playback. Lower-quality video playback means more imperfections and a lower frame rate.
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Tip: Click the following links to see the video sizes recommended in the preceding table: 176x132, 240x180, 320x240 |
The table shows that 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.
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Tip: When resizing a video with Helix Producer, setting the RealVideo preferences to high-quality resize rather than a fast resize yields better results. |
In some cases, you may want your clips to stream at less than the maximum recommended streaming speed listed in the table "Maximum Streaming Rates". In the following cases, you may want to reduce your clip's bandwidth:
How will you deliver your clips to other people? As the following sections explain, how you plan to stream your clips can greatly affect your media production.
Helix Universal Server is the preferred host for streaming presentations. 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. A Helix Universal Server administrator sets up and runs each Helix Universal Server. If you will not be running Helix Universal Server yourself, check the following with your Helix Universal Server administrator:
To deliver clips described in this manual, you'll need RealSystem Server 8, or Helix Universal Server 9. Make sure that your Helix Universal Server can deliver all of the clips that you plan to develop.
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. Make sure that the Helix Universal Server you plan to use has adequate capacity for your needs.
The Helix Universal Server computer may lack the outgoing bandwidth to deliver a lot of high-speed clips simultaneously. If you plan to develop high-bandwidth presentations, confer with the Helix Universal Server administrator about bandwidth limitations.
Your clips typically reside on Helix Universal Server, whereas your Web pages are on a Web server. You'll need to know the URLs for your clips on Helix Universal Server so that you can set up your Ram file URLs and Web page hyperlinks correctly. (Chapter 3 covers these topics in detail.)
The Helix Universal Server administrator can set up many streaming and security features, such as:
If an Internet service provider (ISP) hosts your Web pages, contact the ISP administrator to check out the Helix Universal Server issues described above. Also find out how much disk space you will have for streaming media. Many ISPs allot you a certain amount of disk space on their servers, such as 5 or 10 Megabytes. Although this is a generous amount for Web pages, it's not much for streaming media. A single video clip can easily take up that much space.
Although Web servers can deliver some streaming clips, they don't have Helix Universal Server's ability to synchronize clips and keep long presentations flowing smoothly. When only a Web server is available, you can still deliver multimedia presentations, but you will not be able to use all of the features that Helix Universal Server offers, such as SureStream technology.
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For More Information: RealNetworks Production Guide has a section on Web server limitations in its presentation delivery chapter. |
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©2002 RealNetworks, Inc. All rights reserved.
For more information, visit RealNetworks Click here if the Table of Contents frame is not visible at the left side of your screen. |
