RealSystem G2 gives you the power to create compelling, complex multimedia presentations streamed over a network. It includes RealServer G2, the most advanced streaming media server available, along with RealPlayer G2 and RealPlayer Plus G2, the world's most popular desktop applications for playing streaming media clips. This chapter explains the basics of how you use RealSystem G2 to put together stunning multimedia presentations.
A RealSystem presentation can consist of one clip, such as a single RealAudio clip, or multiple clips played in sequence or in parallel. RealSystem streams these presentations over a network. If you have ever downloaded a video or audio clip to your Web browser, you know that it can take several minutes to receive a clip that plays for a few seconds. In contrast, a clip streamed by RealServer G2 begins to play back almost immediately.
RealSystem G2 gives you many possibilities for combining media clips into presentations. There are two basic types of file formats you can stream with RealSystem G2:
Editing programs typically let you save or export files to a standard, "open" format. Video editing programs usually let you export files to the AVI format or QuickTime. RealSystem can stream several standard formats, but these formats may not be optimized for network streaming.
Formats such as RealAudio and RealVideo are highly compressed formats optimized for network streaming. These formats give the best results. You can convert a file from a standard format to a streaming format with an encoding tool. Some editing programs can also export files directly to streaming formats.
Chapter 4 discusses the audio formats you can stream:
Chapter 5 describes the video formats you can stream:
RealFlash, which pairs Macromedia Flash animation with a RealAudio soundtrack, lets you stream animated presentations. See Chapter 6 for details.
RealSystem presentations can include still images in these formats:
You can also assemble GIF, JPEG, BMP, or STiNG images in a RealPix presentation to create eye-catching slide shows with special effects such as dissolves and zooms. If you have RealPlayer G2 installed, click here to view a RealPix sample. For more information, download RealPix Authoring Guide from http://www.real.com.
RealText streams text at specific times within a presentation. You can use RealText to add subtitles to a video, for example, or lay out text from a live source to create a real-time stock ticker. If you have RealPlayer G2 installed, click here to see a static example of a RealText stock ticker. For details, see RealText Authoring Guide, available at http://www.real.com.
RealSystem easily extends to stream nearly any type of clip or live event. Check http://www.real.com for the availability of plug-ins that let RealSystem stream additional video and audio formats, as well as exciting new types of media.
Most RealPlayer users upgrade when a new version of RealPlayer becomes available. You can generally assume, therefore, that your audience can receive any clip described above. To create presentations playable by older versions of RealPlayer, though, take into account RealPlayer and clip type compatibility. The table below indicates which RealPlayer versions, such as RealPlayer G2 or RealPlayer 5.0, can play which types of clips. RealPlayer 4.0, for example, plays only RealAudio and RealVideo.
Keep in mind that this table covers general clip compatibility, not codec compatibility. Later versions of RealPlayer typically introduce RealAudio and RealVideo codecs not available on earlier versions. RealPlayer G2, for example, can play clips encoded with SureStream codecs. Earlier versions of RealPlayer cannot. So when planning for backwards compatibility, make sure you encode RealAudio or RealVideo clips with a codec playable by your targeted versions of RealPlayer.
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| For more on codecs, see "Choosing RealAudio Codecs" and "Choosing RealVideo Codecs". |
After choosing your streaming media formats, gather content and use your preferred tools to edit your source files. Sound editing software, for example, lets you optimize an audio clip's dynamic range. With video editing software you can set the video's window size RealSystem does not require you to use specific editing tools. Just ensure that your editing tools can save files in streaming formats, or in open formats you can easily convert to streaming formats.
If your editing program does not export files to the streaming format you want, you can use an encoding tool to convert the file. RealNetworks provides free, basic tools for converting popular sound and video formats to RealAudio and RealVideo. It also sells enhanced tools that help you create HTML pages and transfer clips to servers. In addition, plug-ins for popular programs such as Adobe Premiere and Microsoft PowerPoint let you save presentations directly as RealVideo. RealNetworks' encoding tools are easy to use, and let you quickly build the presentation you want.
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| Check http://www.real.com/products/tools/ for the tool that's right for you. |
RealSystem G2 provides virtually unlimited possibilities for streaming media. It does not lock you into a small set of streaming formats or a specific set of tools. In addition to new types of streaming media, RealNetworks' partners and other parties are continually producing new tools that help you put together sophisticated presentations. Check http://www.real.com frequently for information about news media types and tools.
As you create streaming media clips, you need to consider how to keep the clips synchronized to a single presentation timeline. You also need to create presentations for specific bandwidths. These are two important, interrelated steps for producing streaming multimedia presentations.
Because a static Web page has no timeline, images and text download without a preset order. You may notice when browsing a Web page that one image may download partially, then another image begins to appear, then the first image completes, and so on. Images and static text do not have internal timelines, so exactly when a certain image gets to the browser doesn't matter. What matters is that the entire page downloads as soon as possible.
When you stream multimedia, though, clips have timelines and must flow smoothly once they've started to play back. Imagine how jarring it would be for the visual track of a video to play silently for a minute, then pause as its audio track catches up to it a minute later. When you stream multimedia, therefore, it's important that your presentation keeps clips synchronized. There are three aspects of timelines you may work with:
Audio, video, and animation have internal timelines. In a two-minute video, for instance, each frame corresponds to a specific point in a two-minute timeline. Each second of audio meshes with each second of the visual image throughout the clip's overall timeline. Your video, audio, or animation editing program is your main tool for manipulating the clip's timeline, which is part of the fabric of the clip.
With RealPix or RealText, you define timing tags that set when each image or text block appears. Unlike a video clip in which the image should always be moving, images and text can remain stationary for indefinite periods until new images and text replace them. 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.
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| Download RealPix Authoring Guide and RealText Authoring Guide from http://www.real.com. |
A SMIL file assembles your presentation and can include its own timing elements. Timing a presentation can be as simple as starting one clip as soon as another one stops. But you can also use explicit timing commands to delay playback for ten seconds, for example, or start a clip playing at 30 seconds into its internal timeline. SMIL's explicit timing commands are optional, but they give you an extra level of flexibility you may need when putting multimedia clips together.
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| "Writing a SMIL File" provides an overview of SMIL. For specifics on SMIL timing, see "Specifying Timing". |
Any presentation streamed over a network has a bandwidth budget because each person viewing streaming clips has a network connection with a top speed, such as 28.8 Kilobits per second. Even when your clips are perfectly synchronized, the presentation may stall if at some point it requires more bandwidth than the viewer has available. This happens because RealServer needs to transmit at a certain point in the timeline more data than can get through the network connection to RealPlayer.
When you develop a streaming media presentation, you need to consider the bandwidth constraints your audience will have. This is crucial for creating presentations that start to play back quickly and flow smoothly. Web users don't like to wait more than a few seconds for something to happen after they click a link. And if your clips stop and restart frequently, viewers are not likely to stay watching. Fortunately, RealSystem offers sophisticated features that let you create single presentation that look good over slow connections and great over fast ones.
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| Chapter 3 provides the details for considering bandwidth in streaming presentations. |
With your clips in their streaming formats, you put your presentation together with SMIL. Pronounced "smile," SMIL stands for "Synchronized Multimedia Integration Language." A SMIL file is not necessary to stream just one clip. But when you have multiple clips, SMIL's simple mark-up language specifies how and when the clips play. Here are some of the many advantages of using SMIL:
Because RealSystem can stream many media formats, you do not need to merge clips into container formats such as these:
Although RealSystem G2 can stream either of these container formats, using RealSystem streaming formats and putting the presentation together with a SMIL file gives you greater flexibility. To change your presentation, for example, you simply edit the SMIL file rather than merge the clips again into a different container file.
Because the SMIL file lists a separate URL for each clip, you can put together presentations using clips in any locations. You can use a video clip from one server, for example, and an audio clip from another.
A SMIL file can list different language options for clips. To create a video with sound tracks in different languages, for example, you produce one video clip with no soundtrack, then create audio clips in each language. Your Web page needs just one link to the SMIL file. When a visitor clicks that link, the visitor's RealPlayer chooses the soundtrack to receive based on its language preference.
The SMIL file can also list presentation choices for different bandwidths. RealPlayer then chooses which clips to receive based on its available bandwidth. You can thereby support multiple connection speeds through a single hypertext link, rather than separate links for modem users, ISDN users, T1 users, and so on.
Because a SMIL file is a simple text file, you can generate it automatically for each visitor. You can therefore create different presentation parts, then assemble a customized SMIL file based on preferences recorded in the visitor's browser.
The SMIL file lets you easily control the presentation timeline. You can delay an audio track by 2.5 seconds, for example, without changing the encoded audio clip.
When your presentation includes multiple elements, such as two videos playing simultaneously, you can use SMIL layout tags to lay out the clips.
For commercial sites, the SMIL file can insert ads into your presentation, either in a separate ad banner or between clips playing in sequence.
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| Chapter 7 explains the SMIL file syntax. Chapter 9 provides examples of ad insertion. |
When your presentation is complete, you move the streaming media clips and SMIL file to RealServer G2 or a Web server for delivery. You then link your Web page to the SMIL file with an HTML hypertext link. Clicking the link launches RealPlayer, which plays the presentation. You can also play the presentation directly in your Web page through RealPlayer's Netscape plug-in or ActiveX Control. This requires that you add mark-up tags to your Web page to specify how the presentation displays and which RealPlayer controls appear.
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| For more on embedding a presentation in a Web page, see Chapter 8. |
RealServer G2 is the preferred host for RealSystem presentations. Designed specifically to stream multimedia over networks. RealServer keeps multiple clips synchronized and uses several advanced features to ensure that clips stream smoothly under adverse network conditions. While you can use a standard Web server to host some streaming presentations, you will not get the results you'll experience when using RealServer.
A Web server uses the HTTP protocol, as you can see in URLs that begin with http://. The HTTP protocol downloads files without regard to timelines, making clips with timelines more likely to stall. Although RealPlayer can play back clips as they download, the HTTP protocol does not give RealPlayer the ability adjust the download to compensate for changing network conditions.
In contrast, URLs for media clips streamed by RealServer begin with rtsp://, because RealServer uses the RTSP protocol, which is designed specifically to stream clips that have timelines. RTSP lets RealPlayer G2 and RealServer G2 exchange information about a presentation in progress and adjust the streaming data to keep the clips playing smoothly.
When two video clips play side-by-side, for example, RealPlayer uses RTSP to communicate with RealServer about each clip's progress, indicating how much data it needs to keep the presentation synchronized. RealServer can then adjust the data flow, reducing low priority data if necessary to ensure that crucial data gets through. Communication like this is not possible when a Web server sends clips to RealPlayer.
You don't need to know the specifics of RTSP to create great presentations. You just need to ensure that RealServer G2 is available to stream your clips. If only a Web server is available, you can still create multimedia presentations, but you won't be able to use all RealSystem features. In either case, make sure you have a good understanding of RealSystem G2 production as described in this manual before you start creating your clips. This helps ensure that your presentation harmonizes with the server that hosts it.
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| For information on RealSystem features that do not work with Web server hosting, read "Limitations on Web Server Playback". |
Because earlier versions of RealServer do not handle SMIL files and many of the RealSystem G2 media types, make sure you have RealServer G2 available. When you host a presentation on RealServer G2, the RealServer administrator will give you basic URL parameters, such as the server address and its RTSP and HTTP port parameters. The RealServer administrator can also set up many content delivery and security features, such as:
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| RealServer Administration Guide, available at http:// www.real.com, explains RealServer features. |
A RealSystem presentation hosted on RealServer or a Web server launches through a RAM file. This file uses the extension .ram if the presentation plays in RealPlayer directly, or the extension .rpm if it plays embedded in the Web browser. The RAM file is needed because browsers may not be configured to launch RealPlayer when they receive a SMIL file or a certain media clip. But the RealPlayer installation configures browsers to launch RealPlayer as a helper application when the browsers receive a RAM file.
When a visitor to your Web page clicks the presentation link, the visitor's Web browser receives the RAM file. The browser then launches RealPlayer and gives it the RAM file. With the information in the RAM file, RealPlayer can then request the SMIL file (if your presentation uses one) and the media clips. Because the RAM and SMIL files are small, this interaction takes little time.
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| RealServer G2 generates RAM files for you, as described in "Streaming Clips from RealServer G2". With Web server hosting, you write the RAM files yourself. See "Playing Clips from a Web Server". |
Although the main function of RealSystem is to stream media clips over a network, you can also create presentations that play back from a user's local machine. An example is a multimedia-enhanced book, like this online manual, written with HTML and containing links to RealSystem clips. Users then download all the book files to their local machines and play back the media clips in RealPlayer.
In this case, you produce clips as described in this manual, except that you don't have to target specific network bandwidths. When you put the presentation together, you simply use URLs that point to clips on the user's machine instead of on RealServer or a Web server.
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| For more on local URLs, see "Linking to Local Clips". |
With RealPlayer G2 installed, you simply click the presentation link in your Web page. RealPlayer buffers presentation clips for a few seconds, then begins to play the presentation back in its own window or your browser. RealPlayer downloads are available from RealNetworks at http://www.real.com.
Unlike a Web browser, RealPlayer does not store clips in a cache. Copies of streaming clips therefore do not reside on viewers' machines. This helps you keep copyrighted material secure. Optionally, RealNetworks tools let you encode clips so that viewers can record the streamed presentation to their local machines.
RealPlayer can play virtually any streaming clip because of its plug-in technology. RealPlayer plug-ins function like Web browser plug-ins. When RealPlayer receives a streaming RealVideo movie, for example, it uses its RealVideo plug-in to play the streaming data on your computer screen. If RealPlayer doesn't have a plug-in needed to play a certain streaming clip, it downloads that plug-in from the Internet.
Plug-in downloading lets you confidently develop presentations using the latest streaming file types available for RealSystem. If visitors to your Web page don't have a plug-in needed to play your presentation, they can quickly download it and view your presentation. Because RealPlayer is the world's most popular application for playing streaming media, you can be sure that your RealSystem G2 presentation can reach the widest audience possible.
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| For more information about developing RealPlayer plug-ins or building RealPlayer capabilities into another application, visit http://www.real.com. |