Real Audio: Details and Overview 2

Overview

The RealAudio system delivers music and speech over a network in real-time. Real-time delivery means that users do not have to wait while a file downloads; the sound plays as it is delivered. Users have complete control over the sound; they can pause, move forward and back, and start or stop at any time.

The network can be the Internet, an intranet, or any local area network. RealAudio formats are optimized for low- to medium-speed connections including 14.4 and 28.8 Kbps modems and ISDN. Users can also listen to RealAudio files stored on their local computers.

RealAudio Clips

A RealAudio clip is a file or live broadcast containing sound encoded in one of the RealAudio formats. These formats are highly compressed to deliver the best possible sound over a limited-bandwidth connection.

Because there is no one best format for delivering sound, the RealAudio system provides several formats that are optimized differently for different kinds of audio content. You can choose to provide a clip in one or more formats based on the type of content and the available bandwidth. For example, you would use a different format to deliver speech over a 14.4 Kbps modem than you would to deliver music over an ISDN connection.

In addition to the sound contained in the RealAudio clip, the RealAudio system can deliver images and other Web pages that are synchronized with the sound. These presentations are called Synchronized Multimedia.

Components of a RealAudio System

The RealAudio system is a client-server system. The server provides the content to the client over a network. The basic components of a RealAudio system are:

RealAudio Player - The client program that enables users to listen to RealAudio clips..

 

RealAudio Encoder - The program that creates RealAudio clips. The input to this program can be a digitized audio file or a live audio signal.

 

RealAudio Server - The server program that delivers RealAudio clips over a network. One RealAudio Server can deliver clips to many Players at the same time. The server for the District is located at the Dana Center.

 

Web Browser - Netscape, Explorer, etc.

 

Web Server - The server program that delivers Web pages. Typically, RealAudio clips are accessed by clicking a link on a Web page.

RealAudio Files and Metafiles

The RealAudio system uses several file types, each identified by a specific file extension. The files and their file extensions are:

RealAudio clip (.ra) - The sound encoded in the RealAudio format. This file is created with RealAudio Encoder and delivered by RealAudio Server.

 

RealAudio metafile (.ram) - The file that connects a Web page to the RealAudio sound clips. The metafile is located on a Web server (where your web pages are located) and is linked by a Web page. The metafile contains the URL of one or more clips located on a RealAudio Server.

Delivering a RealAudio Clip

The following figure shows the components of the RealAudio system used to deliver a typical RealAudio clip. The numbers in the figure match the numbered steps following the figure.

 
1. The Web browser displays a Web page that contains a link to a RealAudio metafile.

    

2. The user clicks the link. The Web browser requests the metafile from the Web Server.

    

3. The Web server delivers the RealAudio metafile to the Web browser. For files with a .ram file extension, the Web server sets the MIME type of the file to audio/x-pn-realaudio.

    

4. The Web browser looks up the MIME type of the RealAudio metafile. Based on the MIME type, the Web browser starts RealAudio Player as a helper application and passes it the metafile.

    

5. RealAudio Player reads the first URL from the metafile and requests it from RealAudio Server.

    

6. RealAudio Server begins streaming the requested RealAudio clip to RealAudio Player.

Note: No messages pass between RealAudio Server and the Web server. The Web browser provides the URL of the RealAudio clip to RealAudio Player. RealAudio Player does not require a Web browser to function; users can enter the URL of a .ra or .ram file directly into RealAudio Player, or use the Preset or Scan buttons on RealAudio Player Plus.