Before you create and manage content for a RealVideo system, you should understand how the system works. This chapter describes the primary components of RealVideo System and explains how they work together. RealVideo Clips Components of a RealVideo System RealVideo Files and Metafiles Delivering a RealVideo Clip Delivering Synchronized Multimedia Title, Author and Copyright Updating RealVideo Clips Live Encoding and Live Broadcasting RealVideo Clips A RealVideo clip is a file or live broadcast containing sound and video encoded in RealVideo formats. These formats are highly compressed to deliver the best possible sound and video over a limited-bandwidth connection. Because there is no single best format for delivering audio and video, RealVideo system provides several formats that are optimized differently for different kinds of 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 a music video over an ISDN connection. Components of a RealVideo System RealVideo System is a client-server system. The server provides the content to the client over a network. The basic components of a RealVideo system are: RealPlayer - The client program that enables users to see and listen to RealVideo clips. Special purpose player components enable ActiveX and Netscape Plug-in capabilities. RealVideo Encoder - The program that creates RealVideo clips. The input to this program can be a digitized audio clip, a live audio signal, a digitized video clip or a live video signal. RealVideo Tools - The tools programs that can be used to modify RealVideo clips, including RMTools, RMMerge, RMEdit, and RMPaste. RealServer - The server program that delivers RealVideo clips over a network. One RealServer can deliver clips to many Players at the same time. Web Browser - The client program that enables users to find most RealVideo clips. The Web browser is also used to display the visual part of Synchronized Multimedia presentations. RealVideo system works with all popular Web browsers. Web Server - The server program that delivers Web pages. Typically, RealVideo clips are accessed by clicking a link on a Web page. The Web server also delivers the visual part of Synchronized Multimedia presentations. HTTP streaming of RealVideo files enables content providers to stream RealVideo clips from a World Wide Web server. While this method is not as robust, it provides a reasonable method for providing short RealVideo content to a limited number of users. RealVideo System works with all popular Web servers. RealVideo Files and Metafiles RealVideo System uses several file types, each identified by a specific file extension. The files and their file extensions are: RealMedia clip (.rm) - Audio and video encoded to RealVideo format. This file is created with RealVideo Encoder and delivered by RealServer. The .rm files can contain multiple streams, including audio, video, image maps, and events. RealVideo metafile (.ram) - The file that connects a Web page to one or more RealVideo or RealAudio clips. The metafile is located on a Web server and is linked by a Web page. The metafile contains the URL of one or more clips located on a RealServer. RealPlayer Plug-in metafile (.rpm) - The same as RealVideo metafile, but used with RealPlayer Plug-in for Netscape Navigator and Internet Explorer 3.0 and later. RealAudio clip (.ra) - Audio encoded to RealAudio format. This file is created with RealAudio Encoders and works with RealPlayer, RealAudio Player, and RealServer. Delivering a RealVideo Clip The following figure shows the components of RealVideo system used to deliver a typical RealVideo clip. The numbers in the figure match the numbered steps following the figure. RealVideo Delivery System The Web browser displays a Web page that contains a link to a RealVideo metafile. The user clicks the link. The Web browser requests the metafile from the Web Server. The Web server delivers RealVideo metafile to the Web browser. Based on the .ram file extension, the Web server sets the MIME type of the file to audio/x-pn-RealAudio. For files with a .rpm file extension (RealPlayer Plug-in), the Web server sets the MIME type of the file to audio/x-pn-RealAudio-plugin. The Web browser looks up the MIME type of RealVideo metafile. Based on the MIME type, the Web browser starts RealPlayer as a helper application and passes it the metafile. RealPlayer reads the first URL from the metafile and requests it from RealServer. RealServer begins streaming the requested RealVideo or RealAudio clip to RealPlayer. Note No messages pass between RealServer and the Web server. The Web browser provides the URL of RealVideo clip to RealPlayer. RealPlayer does not require a Web browser to function; users can enter the URL of a .ra, .rm or .ram file directly into RealPlayer, or use the Preset or Scan buttons on RealPlayer Plus. Delivering Synchronized Multimedia Synchronized Multimedia delivery works like regular RealAudio or RealVideo delivery, with one extra step between RealPlayer and the Web browser. The following figure shows the components of RealVideo System used to deliver a typical RealVideo Synchronized Multimedia presentation. The numbers in the figure match the numbered steps following the figure. Media Delivery System The Web browser displays a Web page that contains a link to a RealVideo metafile. The user clicks on the link. The Web browser requests the metafile from the Web Server. The Web server delivers RealVideo 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. For files with a .rpm file extension (RealPlayer Plug-in), the Web server sets the MIME type of the file to audio/x-pn-RealAudio-plugin. The Web browser looks up the MIME type of RealVideo metafile. Based on the MIME type, the Web browser starts RealPlayer as a helper application and passes it the metafile. RealPlayer reads the first URL from the metafile and requests it from RealServer. RealServer begins streaming the requested RealAudio or RealVideo clip to RealPlayer. RealServer concurrently notifies RealPlayer when an event should occur. For more information see Using Synchronized Multimedia with Bandwidth Negotiation RealPlayer sends the URL for the event to the default Web browser for viewing. Title, Author, and Copyright RealAudio and RealVideo clips include text strings for the title, author, and copyright. This text is displayed by RealPlayer when the clip is played. Although the player usually labels the text as title, author, and copyright, the player displays whatever text you choose to supply. Enter the title, author, and copyright text when you encode a clip. You can override the values encoded with the clip using the metafile. You can also change the text using RMEdit and RMTools. For information about changing the Title, Author or Copyright text strings in encoded files, refer to Modifying RealVideo File Descriptions. Updating RealVideo Clips When you encode a RealVideo clip, the original file is not modified. RealVideo Encoder creates a new file with a .rm file extension. It is important to note that encoding a RealVideo clip is a one-way process; you cannot convert a RealVideo file back into the original source format. If you want to be able to encode to other formats in the future, you need to archive the original source. It is possible to modify various attributes of RealVideo clips without re-encoding them. For information about changing the Title, Author or Copyright text strings in encoded files; or about enabling or disabling PerfectPlay and Selective Record, refer to Modifying RealVideo File Descriptions. Live Encoding and Live Broadcasting The source of a RealVideo clip can be prerecorded or live input. The encoded RealVideo clip can be stored as a file for later use, broadcast live over a network or it can be simultaneously stored as a file and broadcast live. The last option allows you to archive the live broadcast. All versions of RealVideo Encoder can encode a live input source. Live broadcasting requires a license and RealServer.

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