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Chapter 6. Encoding, Serving, and Streaming Sound with RealAudio

RealAudio is the premier platform for streaming audio and video on the Web. While MP3 and QuickTime may have higher quality audio and video compression, neither provides RealAudio's advanced server functionality, reliability, and administrative tools -- features that are needed to carry out large-scale professional broadcasting. RealAudio not only provides a streaming media delivery format and media player, but its server technology optimizes audio playback over multiple modem connection speeds.

The RealMedia System works behind the scenes to deliver the best quality audio stream to both high- and low-bandwidth users. Interactive short-form audio formats such as Flash, Shockwave, and Beatnik are tailored for sound effects and loops and do not offer features for managing and controlling streams over various connection rates. Flash and Beatnik are also more likely to cause audio drop-outs and error messages when streaming long-form audio files.

Professional developers opt for RealAudio for a number of reasons, including:

In this chapter, we introduce you to the basic components of the RealMedia System and then show you how to encode and stream RealAudio content. We also explore advanced real-world case studies to show you how the technology is used in professional applications.

6.1. The RealMedia System

The RealMedia System is comprised of three core components: RealEncoder, RealServer, and RealPlayer. In addition, RealNetworks provides a suite of RealMedia tools and utilities. This chapter focuses primarily on RealMedia 5.0 components and features. A large portion of your listening audience may not have the G2 plug-in yet. Thus, for many developers, RealAudio 5.0 is still the preferred format. Figure 6-1 illustrates the process of RealMedia creation and delivery including the interaction between server-side and client-side components.

Figure 6-1

Figure 6-1. An overview of the RealSystem 5.0

RealAudio listening guides

To hear RealAudio broadcasts on the Web, check out the thousands of listings on http://www.Broadcast.com or RealNetwork's RealGuide at http://www.real.com/realguide/index.html. The Broadcast.com and RealGuide web sites offer some of the largest directories of RealAudio programming on the Net. Both sites feature business, news, sports, music, politics, and entertainment content. To list your site or event on RealGuide, click on the Add Your Site/Event link at the bottom of the RealGuide home page. Fill out the event questionnaire and enter the URL for your RealAudio content, and a RealGuide reviewer will verify your URL and list your programming in the appropriate category.

In brief, when a listener clicks on a web page that contains a RealAudio link, the web server does not stream the audio file but instead prompts the web browser to start up the RealPlayer application. RealPlayer then requests the audio file from RealServer. RealServer in turn streams media content generated from RealEncoder and RealPublisher. Finally, RealServer keeps track of media usage via the Java performance monitor, log file records, and authentication software. Figure 6-1 also helps to distinguish the process of RealMedia delivery with a dedicated RealServer as opposed to streaming audio from a standard web server.

The RealAudio generation gap


This chapter documents basic RealAudio operations, as found in RealAudio 5.0, the last version of RealNetworks original streaming media platform. RealAudio 5.0 is still widely used for ensuring backwards compatibility with older RealPlayers. Most of the information in this chapter is still relevant to later versions. RealMedia version 6.0 and later represent RealNetworks second generation streaming media platform (G2) with enhanced encoding and playback performance and powerful new multimedia capabilities including support for SMIL. These multimedia features are covered in the next chapter.


RealMedia 7.0 features better server performance and integration of server-side advertisement management features that let RealNetworks customers stream and track their rich media advertising. RealMedia 8.0 represents a major quality breakthrough including the following:

  • Significantly enhanced video quality (VHS quality at 300 to 500 kilobyte throughput)

  • Server support for streaming QuickTime files from a RealServer

  • Remote license management (for system administrators) that lets companies split one license across several machines/servers

  • MP3 streaming directly from the RealServer without using third-party plug-ins

6.1.3. RealPlayer

The last piece of the puzzle is RealPlayer -- the player or "decoder" (shown in Figure 6-3) that receives the incoming audio signal. The RealPlayer decodes incoming audio packets that have been compressed with the RealEncoder. The RealPlayer is free and features random access controls such as scroll, stop, start, and pause. The RealPlayer Plus lets you set custom presets or channels that point to your favorite RealAudio broadcasting sites and record RealAudio clips to your desktop. The G2 RealPlayer Plus includes a graphic equalizer video brightness, contrast, and tint controls (see Chapter 7, "Designing Multimedia Presentations with SMIL and RealSystem G2" for more information about RealSystem G2).

Figure 6-3

Figure 6-3. RealPlayer 5.0 decodes incoming audio packets that are compressed with the RealEncoder.

RealAudio web resources


Visit the RealNetworks Developer Zone web site at http://www.real.com/devzone/index.html. The Devzone's documentation library allows you to access hundreds of pages of online manuals and content creation guides. You will also find an impressive amount of free information including an extensive index of downloadable PDF RealMedia guides, side-by-side comparisons of the latest codecs, software developer kits, and an open forum with answers provided by RealAudio technical experts.


The RealAudio forum is an especially useful resource for finding solutions to a broad range of common problems. You can also read through past issues of the bi-weekly "digested" RealAudio forum to look for previously posted workarounds and solutions. You can even look through a searchable archive built by the media experts at Stanford University's MedNET site (http://mednet.stanford.edu/realforum.html) that contains all the previously posted RealAudio forums.


RealNetworks also provides a comprehensive content creation and authoring products site (http://www.real.com/products/index.html?src=eml,hardware,productsmain) with more than 20 free and commercial media products for Macintosh, Windows, and Unix from RealNetworks and other industry-leading companies.

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