previous next

Chapter 2: Presentation Planning

A streaming presentation may be as basic as a single clip, or as complex as dozens of clips and HTML pages coordinated to display at different times. No matter how simple or complicated your presentation, you'll need to plan your media production so you can work effectively and reach your target audience. This chapter explains the basics of how to put streaming media presentations together. If you are not yet familiar with streaming media and RealOne Player, see also Appendix A.

Tip: For a streamlined approach to media production, download Introduction to Streaming Media from

Step 1: Decide How to Deliver Clips

The first step in creating a streaming presentation is to consider the last step: how will you deliver your clips to other people? How you plan to stream your clips can greatly affect your media production.

Helix Universal Server Streaming

Helix Universal Server is the preferred host for RealOne Player 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:

  1. What server version is available?
  2. To deliver the clips described in this guide, you'll need Helix Universal Server or RealSystem Server 8, rather than any of the earlier versions. Make sure that your Helix Universal Server can deliver all the clips that you plan to develop.

  3. How many streams can Helix Universal Server deliver?
  4. 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.

  5. Are there any bandwidth constraints?
  6. 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.

  7. Where will your clips reside?
  8. 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 Web page hyperlinks correctly.

  9. Do any Helix Universal Server features need to be set up?
  10. The Helix Universal Server administrator can set up many streaming and security features, such as:

Using Helix Universal Server through an Internet Service Provider

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.

Web Server Downloading

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 RealOne Player offers.

For More Information: If you plan to deliver clips with a Web server, read "Limitations on Web Server Playback".

Local Playback

You can also create presentations that play back from a user's local computer. An example of this is a multimedia-enhanced book, like this online manual, written with HTML and linking to clips. Users download the files to their computers, playing back the media clips with RealOne Player. In this case, you produce clips as described in this guide, except that you don't target specific network connection bandwidths. In the HTML pages, URLs point to clips on the user's computer instead of on Helix Universal Server.

For More Information: For more on local URLs in SMIL files, see "Linking to Local Clips". See also "Launching RealOne Player with a Ram File".

Step 2: Learn the RealOne Player Interface

RealOne Player integrates streaming media with HTML pages simply and effectively. Because previous versions of RealPlayer did not natively display HTML pages, linked pages opened in the viewer's default Web browser, which split the presentation between separate applications. RealOne Player closes this divide, benefitting both the viewer, who does not have to switch between applications to watch an integrated presentation, and the presentation author, who can more easily coordinate streaming media with Web pages.

A thorough understanding of how RealOne Player's various panes let you coordinate streaming media with HTML pages helps you to envision the types of presentations that you can deliver. This section covers these interface elements, and then discusses the types of production techniques that you can use to tie your media and your HTML pages together. RealOne Player supports several different production techniques, suitable for everyone from beginning media authors to Web professionals.

The Three-Pane Environment

The following figure illustrates the RealOne Player environment, which is based on the metaphor of "play/more/explore." Here, the Media Playback pane plays streamed or downloaded clips. The Related Info pane gives the viewer more information about the presentation. The detachable Media Browser pane and any secondary browsing windows let the viewer explore the World Wide Web. This design gives you one pane for playing media, one pane for displaying small HTML pages related to the media, and one or more windows for showing large Web pages, such as your home page.

RealOne Player Three-Pane Environment with a Secondary Browsing Window

RealOne Player Three-Pane Environment with a Secondary Browsing Window

The Media Playback Pane

The media playback pane hosts media clips and includes buttons for play, pause, rewind, volume control, and so on. Any streaming or downloaded media playable in RealOne Player can display in this pane. This includes the core clip types and markup languages described in "Step 3: Choose Clip Types and Gather Tools". In addition, RealOne Player can play many other media types, including MPEG audio and video.

Media Playback Pane Sizing

The media playback pane automatically scales to the size of the playing media. If no HTML page displays in the related info pane as media plays, the media playback pane appears centered above the media browser pane as shown in the following figure. The media browser pane's resize handle allows the viewer to adjust the relative heights of the top and bottom halves of the three-pane environment.

Media Playback Pane Centered Above the Media Browser Pane

Media Playback Pane Centered Above the Media Browser Pane

Tip: As explained in "Making Room for the Related Info Pane", you can use SMIL to display the media playback pane at the left side of the RealOne Player window instead of in the center.

Media Playback Pane Alone

If the viewer has detached or closed the media browser pane, the media playback pane encloses the playing media, as illustrated in the next figure. This gives the viewer access to media in a smaller pane that includes just the necessary controls for adjusting media playback.

Media Playback Pane Without the Media Browser Pane

Media Playback Pane Without the Media Browser Pane

Media Playback and Related Info Panes

If a media presentation opens an HTML page in the related info pane, the media playback pane automatically expands to display both the media and the HTML page, as shown in the next figure.

Media Playback Pane With the Related Info Pane

Media Playback Pane With the Related Info Pane

Visualizations for Audio-Only Clips

When playing audio-only clips, the viewer can display in the media playback pane a visualization, such as an audio analyzer consisting of bars that rise and fall in response to the strength of various audio frequencies.

A Visualization in the Media Playback Pane

A Visualization in the Media Playback Pane

Double-Size and Full-Screen Modes

Content authors and viewers can also play media at double-size or full-screen. In full-screen mode, the media playback pane expands to fill the entire computer screen. In this case, no HTML pages in the related info or media browser panes display until the presentation ends, or the viewer exits full- screen mode.

The Related Info Pane

The related info pane, which is also called the "context pane," appears to the right of the media playback pane. It's designed to display small HTML pages that supplement media clips. These pages might contain album cover art, copyright information, advertisements, and so on. Although using the related info pane is not required, displaying supplemental HTML pages in this pane greatly enhances the viewing experience. The related info pane can display any HTML page content supported by Microsoft Internet Explorer version 4 or later.

Because the media playback and related info panes are separate, you can easily open multiple HTML pages as a presentation plays, displaying each page at a specific point in the media timeline. You can thereby update the related info pane simply by opening a new HTML page. In contast, when you embed media in a Web page, updating the page as the media plays can require complicated scripting. RealOne Player thereby lets you focus on your media, and display any number of supplemental HTML pages by using simple production techniques.

Note: Because no divider marks the boundary between the media playback and related info panes, it's easy to blend the panes by setting the same background colors. For the related info pane, you set the background color in the HTML page. Later sections in this guide explain how to set the media playback pane's background color through various methods.

Related Info Pane Sizing

The RealOne Player production techniques described in this guide let you set the size of the related info pane. If you do not specify a size, the pane uses a default width of 330 pixels, and a height the same as the media playing in the media playback pane. If the page content is too large for the specified size, the pane displays scroll bars the same as a standard browser window.

The related info pane's size is fixed for the presentation's duration. As a clip or SMIL presentation plays, the first URL that opens in the related info pane sets the pane size. If a subsequent URL opens in the related info pane while the same clip or presentation plays, any sizing information in that URL is ignored. You can specify a new related info pane size, though, when starting a new clip or SMIL presentation.

Tip: Because of the generally small size of the related info pane, using frames in this pane is not recommended.

Media Clips Set the Minimum Height

You can set the related info pane to a height greater than the media, but not smaller. If your media is 300 pixels high, for example, your related info pane will be 300 pixels high even if you specify a shorter height, such as 200 pixels. However, you can create a related info pane that is taller than your media, such as 400 pixels. In this case, RealOne Player centers the media playback pane vertically alongside the related info pane.

Media Browser Pane Can Override the Width

When the bottom media browser pane is attached to the top two panes, it may increase the width of the related info pane. Suppose that you play a media clip that is 200 pixels wide, and you specify a related info pane width of 300 pixels. If the media browser pane is not attached, the width of the top two panes is 500 pixels. If a 600-pixel-wide media browser pane is attached, though, RealOne Player adds 100 pixels to the related info pane width to increase the overall width of the top panes to 600 pixels.

HTML Page Caching

RealOne Player caches the HTML pages that display in the related info pane for the duration of a presentation. It deletes this cache when a new clip plays. RealOne Player does not normally cache media clips that play in the media playback pane. However, when you use SMIL, you can make RealOne Player cache small clips, such as images, that display in the media playback pane.

For More Information: See "Caching Clips on RealOne Player" for more information about RealOne Player's CHTTP caching protocol for small media clips.

The Media Browser Pane

The media browser pane can attach to, or detach from, the media playback and related info panes. When attached, it appears below the two other panes. Detached, it appears as a stand-alone window that the viewer can resize and close independently of the media playback and related info panes. Sending an HTML page URL to a closed media browser pane reopens the pane, however.

Through the media browser pane, RealOne Player users can surf the Web, play CDs, access their personal media libraries, transfer clips to portable players, and so on. Presentation authors can also use this pane to display Web pages associated with a streaming presentation. The pane supports any content playable in Microsoft Internet Explorer version 4 or later, including Javascript. You might use this pane to display your home page after a media presentation plays, for example.

`Now Playing' List

In the left side of the media browser pane, viewers can display a clickable "Now Playing" list. When the viewer plays a media clip or presentation, the clip or presentation title displays in this list. Additionally, the viewer can build a clip list by dragging media links from an HTML page displayed in the related info or media browser pane.

RealOne Player `Now Playing' List

RealOne Player `Now Playing' List

Secondary Browsing Windows

Like most Web browsers, RealOne Player can display any number of additional browsing windows, which are independent of the three-pane environment. You can display Web pages associated with your presentation in secondary browsing windows, for example. Displaying full Web pages in the main media browser pane is preferable in most cases, though, because many viewers are likely to have that pane already attached to the media playback and related info panes. Additionally, only the media browser pane includes the "Now Playing" list.

Using Media Clips to Open HTML Pages

You can use three different techniques to open URLs in an HTML pane as a media clip plays. These techniques allow you to create "media-driven" presentations, in which supplemental information displays in the HTML panes at a specific point in the media timeline, or in response to viewer interaction with clips.

Appending HTML URLs to Clip URLs in a Ram File

You typically use a Ram file, which uses the extension .ram, to launch media clips that play in RealOne Player. As the section "Passing Parameters Through a Ram File" explains, you can add to the Ram file the URLs for HTML pages that open in the related info or media browser pane. This Ram file method is easy to use, and is well-suited for simple presentations, such as a single RealVideo clip that displays an HTML page as it plays.

Embedding HTML URLs Into a Clip

When you create a RealVideo or RealAudio clip with Helix Producer, you can write an events file that defines one or more URLs that open in a RealOne Player HTML pane at certain points as the clip plays. You then use a utility that embeds the events into the clip. Whenever you stream the clip, the encoded URLs open automatically. Introduction to Streaming Media provides more information about this production technique.

Using SMIL to Coordinate Clips and HTML Pages

To lay out and synchronize multiple media clips, you use Synchronized Multimedia Integration Language (SMIL). A SMIL presentation always plays in the media playback pane, but it can also open HTML pages in the other panes. Using SMIL gives you more control over HTML display than using a Ram file, or encoding URLs directly into clips. You can learn about SMIL starting with Part IV of this guide. Chapter 15 covers SMIL's hyperlinking attributes.

Controlling a Presentation Through HTML Pages

Through HTML pages displaying in the related info pane or media browser pane, you can control the media displaying in the media playback pane, as well as open new HTML pages. These production techniques, which you can mix with the media-based techniques described previously, allow you to create "user-driven" presentations, in which clips and HTML pages display according to viewer action within the HTML panes.

Linking One HTML Pane to the Other

The most basic way to link one HTML pane to another is through a simple hypertext link in the form <a href>. You can open a new HTML page in the media browser pane through a hypertext link in the related info pane by adding a target="_rpbrowser" attribute to the <a href> tag:

<a href="URL" target="_rpbrowser">

Any other target name will open the HTML page in a secondary window that is detached from the basic three-window environment.

You should not attempt to open an HTML page in the related info pane with a simple link in the media browser pane, however, because the related info pane URL requires sizing information that you cannot pass in the link. However, the Javascript/VBScript methods described below let you pass this information.

Launching a Clip with an HTML Page Link

If you link to a Ram file with a simple <a href> link as described in "Launching RealOne Player with a Ram File", the clip or SMIL presentation listed in the Ram file automatically plays in the media playback pane. You do not need to use any additional window targeting attributes. To avoid a file download dialog, though, you can use the Javascript or VBScript methods to play clips when the viewer clicks certain links.

Using Javascript and VBScript Methods

RealOne Player supports several methods that work with both Javascript and VBScript. Used in HTML pages displaying in the related info pane or media browser pane, these methods give you more control than standard <a href> links. They are intended for HTML pages displaying in the RealOne Player environment, however, and not for HTML pages rendered by other browsers.

The Javascript/VBScript methods are well-suited for creating Internet-based audio and video jukeboxes, for example. Using these methods, you can create interactive presentations that add clips to the "Now Playing" list, for example, or play clips based on viewer interaction with forms or elements displayed in the related info or media browser pane.

For More Information: For information about using Javascript and VBScript methods with RealOne Player, see RealOne Player Scripting Guide.

Step 3: Choose Clip Types and Gather Tools

RealOne Player gives you many possibilities for creating streaming media. Your presentation may consist of a single clip, or several clips that play together. As described in the preceding section, RealOne Player can also display HTML pages while clips play. After you decide what types of clips you want to stream, you'll need to gather the production tools used to make the clips.

Audio and Video

RealAudio and RealVideo are the most popular streaming media formats. To produce them, you run an encoding tool that takes audio or video input from one of these sources:

Audio and Video Production Tools

A streaming RealAudio or RealVideo clip results from gathering, editing, and encoding audio or video input. To carry out the initial steps of gathering and editing content, you'll need the following:

Producing RealAudio and RealVideo does not require that you use specific microphones, cameras, capture cards, or editing tools. Just ensure that your editing tools can save files in formats that you can easily convert to streaming formats with your encoding tool.

For More Information: Chapter 3 and Chapter 4 describe the RealAudio and RealVideo formats in detail.

RealAudio and RealVideo Encoding Tools

Some editing programs can export digitized audio and video directly to RealAudio or RealVideo. If your editing program cannot export clips, or you don't want to use this feature, you can use a RealNetworks tool to encode clips from files in standard formats such as WAV, AVI, QuickTime, and MPEG. 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.

Helix Producer Creates Streaming Clips

Helix Producer Creates Streaming Clips

For More Information: For more information about Helix Producer, see "Getting Production Tools". You can also learn more at tml.


When you want to combine two or more clips into a single presentation, you use SMIL. Pronounced "smile," SMIL is a simple markup language that tells RealOne Player how to lay out and play your clips. You can use any word processor or text editor to write SMIL. To learn SMIL, start with Chapter 8. For basic information about SMIL syntax, see "Writing SMIL Files".


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. See Chapter 5 for details about producing Flash animation for RealOne Player. Learn more about Flash from Macromedia's Web site at:

RealOne Player also plays animations in the Scalable Vector Graphics (SVG) format. You can learn more about SVG at Adobe Corporation's Web site:


Still images can display in the media playback pane, as well as the media browser and related info panes. For images displayed in the media playback pane, you can use any of the following formats:

Images in SMIL Presentations

To add images to streaming presentations as backgrounds or buttons, for example, simply incorporate the images by using SMIL. This way, you can specify exactly where images appear in relation to your clips. You can also use SMIL to turn images into hyperlinks.

RealSlideshow Presentations

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. RealNetworks' partners will even host your streaming slideshow. Get RealSlideshow at:

RealPix Markup

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. Chapter 7 explains the RealPix markup language.


As the section "Adding Text to a SMIL Presentation" explains, there are three ways to add text to a SMIL presentation that displays in the media playback pane. You can display a plain text file (.txt), add text directly to your SMIL file, or display a RealText clip (.rt), which displays text at specific times within a presentation. As well, you can display HTML text in the RealOne Player related info and media browser panes. Chapter 6 describes RealText markup.

Autoupdate Feature

RealOne Player's plug-in and autoupdate technologies ensure that your clips can reach the widest audience possible. RealOne Player plug-ins function like Web browser plug-ins. If RealOne Player doesn't have a plug-in needed to play a particular streaming clip, it downloads that plug-in. RealOne Player can even use its autoupdate technology to upgrade itself to a new version when necessary.

The following figure illustrates the process for downloading a new plug-in. In step 1, RealOne Player encounters an unknown clip type. Next, it contacts RealNetworks to determine if a plug-in for that type of clip is available. The RealNetworks server then downloads the new plug-in to RealOne Player, as shown in step 3. In the final step, RealOne Player plays the clip using the new plug-in.

RealOne Player Downloads Plug-ins it Needs from the Internet

RealOne Player Downloads Plug-ins it Needs from the Internet

Compatibility with Earlier Versions of RealPlayer

Plug-in and autoupdate technologies were introduced with RealPlayer G2. Earlier versions of RealPlayer cannot upgrade themselves, so they cannot play all the clips described in this production guide. Generally, you don't need to be concerned with backward compatibility because most RealPlayer users upgrade to the latest release. The following table summarizes which versions of RealPlayer offer which features. RealPlayer 4.0, for example, plays only RealAudio and RealVideo.

Supported Features in RealOne Player and Earlier RealPlayer Versions
Feature RealOne 8 7 G2 5 4 3 2 1
RealAudio streaming X X X X X X X X X
RealVideo streaming X X X X X X
Flash 2.0 streaming X X X X X
Flash 3.0 and 4.0 streaming X X
RealPix streaming X X X X
RealText streaming X X X X
SMIL 1.0 presentations X X X X
SMIL 2.0 presentations X
Plug-ins for additional clip types X X X X
Autoupdate X X X X

This table covers general clip compatibility, but other factors may prevent backwards compatibility. For example, not all RealAudio and RealVideo codecs are compatible with earlier versions of RealPlayer. If you are concerned about backwards compatibility, make sure that you understand the specifics of each clip type as described in the various chapters of this guide.

Protection of Copyrighted Content

Unlike a Web browser, RealOne Player does not store media clips in a disk cache, or allow users to copy or download still images. This helps you keep copyrighted material secure when you stream clips from Helix Universal Server, though not from a Web server. A Helix Producer option lets you encode RealAudio and RealVideo clips so that viewers can record the clips on their computers. For managing copyrighted media, RealNetworks has available a Media Commerce Suite, which you can read about at the following Web page:

Step 4: Develop a Bandwidth Strategy

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 developing 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 devise ways to deliver good clips to users with slow connections, and great clips to those with fast connections.

Presentation Data Must Fit RealOne Player's Bandwidth

Presentation Data Must Fit RealOne Player's Bandwidth


For each streaming clip, RealOne Player keeps a "buffer" that acts as a data reservoir. Data enters the buffer as it streams to RealOne Player, leaving the buffer as RealOne Player plays the clip. The buffer helps ensure that lapses of available bandwidth don't stall the presentation. If network congestion halts the flow of data for a few seconds, for example, RealOne Player keeps the clip playing with the buffered data. Your goal is to minimize initial buffering and eliminate rebuffering.

Initial Buffering (Preroll)

RealOne Player buffers a few seconds of data before a clip plays. Also called "preroll," initial buffering is required for every clip. Developing clips that use an appropriate amount of bandwidth keeps preroll to an acceptable level. You want preroll to be low—less than 15 seconds for each clip. RealAudio and RealVideo encoding tools set a low preroll for you. With other clips, though, how you create the clip determines its preroll.


When clip data has stopped coming in and the clip buffer is empty, RealOne Player has to halt clip playback to store data again, or "rebuffer." Sometimes this is unavoidable because the viewer's available bandwidth drops for too long. When developing a multiclip presentation, though, you need to consider timelines carefully so that you don't inadvertently cause rebuffering, which can happen if too many clips fight for too little bandwidth.

Audience Bandwidth Targets

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 require frequent rebuffering. The following table recommends maximum streaming speeds for common network connections. To reach 56 Kbps modems, for example, a presentation should stream no more than 34 Kb of data per second.

Maximum Streaming Rates
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

For any other connection speed, calculate the maximum streaming speed as:

Multiclip Presentations

When several clips are played together, their streaming speeds added together should not exceed the connection maximum. For example, RealPix and RealAudio clips streaming at 12 and 8 Kbps, respectively, can play in parallel over 28.8 Kbps modems because together they stream at 20 Kbps. However, they cannot play back together if they stream at 12 and 16 Kbps, respectively, because the 28 Kbps total streaming speed leaves the modem no bandwidth for overhead. Such a presentation would likely require frequent rebuffering.

Streaming at Less than the Maximum Speed

Your presentations do not have to stream at the maximum speeds listed in the preceding table. In some cases, you may want your clips to stream at less than the maximum:

Clip Bandwidth Characteristics

To reach your target audiences with your clips, you need to understand your clips' bandwidth characteristics.

RealAudio and RealVideo

A RealAudio and RealVideo encoding tool can turn your source audio or video file into a clip that streams to any target connection with little preroll. But if the tool 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 results. To ensure good-quality playback, keep your streaming bandwidths in mind when creating source files, especially when you plan to reach dial-up modem users.

For More Information: See "Understanding RealAudio" and "Understanding RealVideo".


Macromedia Flash streams well at low bandwidths, making it an attractive alternative to video. Low streaming speed doesn't affect Flash's visual quality as it can with video. At low bandwidths, though, you may not be able to include as many items in your animated scenes as when streaming at high bandwidths. After you develop a Flash clip for RealOne Player, you tune it to stream at a specific bit rate. For more on this, see "Flash Bandwidth Characteristics".

RealText and SMIL

Because RealText and SMIL files are plain text, they use little bandwidth. You generally don't need to be concerned about how they affect a presentation's bandwidth consumption.

RealPix (Slideshows)

RealPix bandwidth use depends on the image sizes and how soon each image must appear in the clip's timeline. At higher bandwidths, you can use larger images and display them at shorter intervals. By varying image size and the RealPix timeline, you gain a lot of control over bandwidth use. RealSlideshow always ensures that images stream at a rate appropriate for your target audience. If you write RealPix markup by hand, though, you need to balance bandwidth, image sizes, and the slideshow timeline.

For More Information: See "Managing RealPix Bandwidth".

Images in SMIL Presentations

JPEG, GIF, or PNG images in a SMIL presentation stream at 12 Kbps. See "Setting a Clip's Streaming Speed" for instructions on changing this streaming bit rate.

Reaching Multiple Audiences

To provide good content for users with slower connections, and great content for those with faster connections, you can use two methods, combining them if needed:

Either way, you add to your Web page just one link for all visitors. You don't need separate links for dial-up modems and DSL connections, for example.

Tip: Helix Producer Plus, which you can purchase and download from tml, installs a bandwidth simulator in RealOne Player that you can use to test different audience speeds for a presentation streamed by Helix Universal Server.

SureStream RealAudio and RealVideo

Using SureStream technology, you can encode a RealAudio or RealVideo clip for multiple bandwidths. For example, you can encode a single RealAudio music clip for 28.8 Kbps modems, 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, as shown in the following illustration.

SureStream Clip Encoded for Multiple Bandwidths

SureStream Clip Encoded for Multiple Bandwidths

Helix Universal Server and RealOne Player can even adjust this 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. RealOne Player doesn't need to rebuffer data during this shifting.

Switching Bandwidths During Network Congestion

Switching Bandwidths During Network Congestion

Switching Between Multiple Clips with SMIL

Only RealAudio and RealVideo clips can stream at multiple bandwidths. You can create multiple versions of other clips, though, each for a different bandwidth. RealOne Player then chooses which clip to play based on a SMIL bandwidth parameter. The following illustration shows a SMIL file that lists separate high-bandwidth and low-bandwidth RealPix clips. Each RealOne Player evaluates the SMIL file and chooses the RealPix clip appropriate for its connection speed. Both presentations use the same SureStream RealAudio clip, though, which has been encoded internally for multiple bandwidths.

Bandwidth Choices through a SureStream Clip and SMIL

Bandwidth Choices through a SureStream Clip and SMIL

When you use SMIL for bandwidth choices, Helix Universal Server cannot downshift to a lower-bandwidth clip group the way it can downshift to a slower SureStream stream. Helix Universal Server employs other techniques, though, to compensate for network congestion. Its stream thinning capabilities enable it to drop low-priority data to decrease the presentation bandwidth temporarily. When the network congestion clears, Helix Universal Server continues to stream all the presentation data.

For More Information: "Switching Between Bandwidth Choices" explains how to use SMIL to designate different bandwidth groups.

Step 5: Organize the Presentation Timeline

Every streaming media clip has a timeline. A RealAudio clip may play for five minutes, for example, giving it a five-minute timeline. When clips are streamed together, you have a presentation timeline as well. Before producing clips, plan the presentation timeline. Among other things, the timeline can determine the order in which you produce clips. A well-conceived timeline also helps ensure that clips do not overload a connection's bandwidth and cause rebuffering.

Timeline Considerations

When you assemble a streaming media presentation, you can manipulate various aspects of clip timelines.

Clips with Internal Timelines

Audio, video, and animation have internal timelines. In a 10-minute video, for instance, each frame corresponds to a specific point in a 10-minute timeline. Each second of audio meshes with each second of the image throughout the clip's overall timeline. Your video, audio, or animation software is your main tool for manipulating the clip's timeline, which is woven into the fabric of the clip.

Clips with Variable Timelines

With RealPix or RealText, you use the markup language to control when each image or text block appears, and how long it lasts. When combining clips, it's typically easier to produce audio, video, or animation first. Then set the RealPix and RealText timelines to coordinate with those clips.

SMIL Timing Commands

A SMIL file can include its own timing elements. Timing a presentation with SMIL can be as simple as having one clip start as soon as another one stops. But you can also use commands to delay playback for 10 seconds, for example, or to have a clip start playing 30 seconds into its internal timeline. SMIL's timing commands are optional, but they give you the flexibility you may need for some presentations.

For More Information: For more on SMIL timing, see Chapter 13.

Timelines for Multiclip Presentations

For presentations that include multiple clips, consider how to group clips without overloading an audience's connection bandwidth. The following illustration shows poor timeline planning. At various points, a video and a slideshow clip playing together exceed the connection's maximum streaming speed, which is represented below by the dashed line. Illustrated by the solid line, bandwidth use peaks again when the second video clip begins to play before the first video clip finishes. This presentation requires a high preroll for clips and would likely result in rebuffering at peak points.

Poor Bandwidth Use in a Multiclip Presentation

Poor Bandwidth Use in a Multiclip Presentation

The next illustration shows better timeline planning and bandwidth management. The presentation starts with a low-bandwidth text clip that does not interfere with the streaming of the images in the image slideshow. A video clip starts after the slideshow has streamed all of its images and does not need any more bandwidth. The second video clip starts after the first video clip has ended, so the two clips do not compete for bandwidth.

Improved Bandwidth Use in a Multiclip Presentation

Improved Bandwidth Use in a Multiclip Presentation

Timeline Management

When developing a streaming presentation, keep the following in mind:

Step 6: Get Started With Production

When you've decided how you'll stream clips, chosen clip types and tools, developed a bandwidth strategy, and planned a timeline, you're ready to start creating streaming presentations. The following sections point you to the chapters you should read to carry out certain jobs. Also, be sure to familiarize yourself with this guide's appendixes. Appendix B, for example, points you to specific information about performing specific tasks. The markup appendixes summarize all tags, helping you to locate features quickly.

Tip: This guide does not explain how to use any specific tools, such as Helix Producer or Macromedia Flash. Be sure to have the documentation for your production tools handy as you develop your clips.

I plan to stream just audio and video clips.

Read Chapter 3 and Chapter 4 to learn about RealAudio and RealVideo, respectively, and to pick up general audio and video production tips. Refer to your Helix Producer User's Guide for instructions on running Helix Producer to encode the streaming clips. Chapter 21 explains how to write a Ram file that links your clips to a Web page.

I want to open HTML pages with my audio and video clips.

The section "Passing Parameters Through a Ram File" explains how to open HTML page through simple parameters listed in a Ram file. If you need more functionality, you can write a SMIL file to open any number of Web pages at any time. Chapter 8 explains the basics of SMIL, and Chapter 15 covers SMIL's extensive hyperlinking capabilities.

I want to embed my audio and video clips in a Web page.

Chapter 20 explains embedding markup. To extend the basic embedded functionality using Javascript or VBScript, see RealOne Player Scripting Guide.

I want to stream Macromedia Flash animation.

Chapter 5 provides tips for making Flash animation stream well. Consult your Flash documentation for instructions about using the Flash application.

I want to create a slideshow.

Chapter 7 explains the RealPix markup for streaming still-image slideshows. If you want to combine your slideshow with another clip, such as an audio soundtrack, you'll need to use SMIL.

I want to learn about SMIL.

Start with Chapter 8 to learn the basics of SMIL. Part V and Part VI explain the basics of SMIL layout and timing. Part VII takes you through the more advanced SMIL features.

RealNetworks, Inc. ©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.
previous next