Chapter 5: RealText Broadcast

Because RealServer can also broadcast RealText live, RealText is an ideal solution for delivering live stock market information or breaking news, for example. Because it is a true streaming server, RealServer streams the data as it comes in, instead of downloading blocks of data to users' computers for later display. This chapter explains how to use the RealText broadcast application included with this manual.

	Additional Information
	RealSystem G2 Production Guide provides an overview of broadcasting. For more on configuring a broadcast, see RealServer Administration Guide. Both are available at http://service.real.com/help/library/encoders.html.

Broadcast Application

You can broadcast RealText to multiple viewers with an application included in the utils directory of this manual. The broadcast application runs on any Windows 32-bit operating system. Its C++ source code is publicly available, though, and you can compile it on a different operating system as noted in "Developing a Custom RealText Broadcast Application".

The RealText broadcast application connects to RealServer G2 and polls a specified directory for an updated RealText file. When it finds an updated file, it sends the file to RealServer, which broadcasts the file contents to the connected RealPlayers.

	Tip
	Available at http://www.real.com/products/tools/, RealNetworks tools let you broadcast RealAudio and RealVideo as well. For information on broadcasting RealPix, download RealPix Authoring Guide from http://service.real.com/help/library/encoders.html.

Installing the RealText Broadcast Application

The RealText broadcast application comprises the exlvtxt2.exe executable file and a few DLLs. These files must reside together, but you can move them from the utils directory to any directory on the RealText broadcast machine. You can broadcast on the RealServer G2 machine or any Windows 32-bit machine with a network connection to RealServer G2. RealText broadcast requires minimal system resources, but RealNetworks recommends using a Pentium 133 MHz or faster processor with at least 32 Megabytes of memory.

	Tip
	The RealText broadcast application consumes unused CPU for monitoring purposes but releases CPU as other processes need it. On an otherwise idle machine, CPU use for RealText broadcast may seem high, but the actual CPU requirement for broadcasting is small.

Creating a Broadcast RealText Clip

Create a RealText clip for broadcast as a simple text file. Use the RealText mark-up tags described in "Text Tags" to format the display text. The file should not have <window> and </window> tags. You set window attributes such as type, width, and height when you start the broadcast application. RealServer sends these attributes to each RealPlayer when it connects to the broadcast.

Tips for Creating Broadcast RealText Files

Here are some pointers on using RealText mark-up when broadcasting a file:

• Start a new input file with the <clear/> tag to clear the existing text in the RealPlayer window. Do not use a <clear/> tag in the middle of an input file, though. In a broadcast, a <clear/> tag does not need to follow a <time begin.../> tag.

• Avoid using <time.../> tags to specify when text appears. Timing elements specify offsets from the start of the broadcast, not from the receipt of the RealText update that includes the elements. Using timing tags can therefore cause unexpected results.

• Keep RealText broadcast files small and broadcast them in a "real time" manner. Do not send large files and use RealText timing tags to delay when the text appears in the RealPlayer window.

Setting the Broadcast URL

Consult with the RealServer administrator to determine the URL for the RealText broadcast. If you are linking a Web page directly to the RealText broadcast, the URL may look like this:

<a href="http://realserver.company.com/ramgen/encoder/media/news.rt">...</a>

This URL includes two virtual directories. The ramgen virtual directory makes RealServer launch RealPlayer without a separate RAM file. The encoder virtual directory specifies a broadcast coming in on a certain port of RealServer rather than an actual file existing on a file system. The RealServer administrator sets up these virtual directories.

If you use a SMIL file, the Web page URL to the file may look like this:

<a href="http://realserver.company.com/ramgen/media/daily.smi">...</a>

Within the SMIL file, you'll have an RTSP link to the RealText broadcast:

<textstream src="rtsp://realserver.company.com/encoder/media/news.rt"/>

	Additional Information
	For more on using SMIL and specifying URLs for media clips, see RealSystem G2 Production Guide, available at http://service.real.com/help/library/encoders.html.

Using SMIL, you can embed a RealText broadcast in a multiclip presentation. You might create a RealVideo clip region and a RealText region that displays breaking news, for example. The SMIL file uses the broadcast URL for the text and a standard URL for the on-demand RealVideo clip. Each person who views the presentation sees the video from its normal beginning, but joins the RealText broadcast in progress.

Starting the RealText Broadcast Application

To run the RealText broadcast application, start the Windows DOS prompt and move to the directory that holds the application. Then start the application as shown in this example:

c:\RealText\Broadcast> exlvtxt2.exe

The application prompts you for a number of parameter values that the following table describes. Enter all values without quotation marks.

Moving a RealText File to the Broadcast Directory

Once started, the broadcast application checks the designated directory with the specified polling frequency for an updated version of the RealText input file. You can place a new file in the directory manually or use any automated method, such as a database query, to create the file. All file updates must use the same input file name specified during application start-up.

The RealText broadcast application resends prior data every three seconds when there is no new data. If you update the input file at 5 and 7 minutes into the broadcast, for example, a viewer joining the broadcast at the 6-minute mark receives the data originally sent at the 5-minute mark within three seconds. That viewer's RealPlayer then ignores all further resends and next displays the file update broadcast at the 7-minute mark.

Stopping the Broadcast Application

To stop the RealText broadcast stream, update the RealText input file so that it has a dollar sign ($) as its first character. Text can follow the dollar sign, but it is ignored:

[file start]
$ ignored text
[file end]

This file is not broadcast, but causes RealServer to terminate the broadcast stream. It also shuts down the broadcast application console window on the broadcast machine.

	Warning
	Do not stop the RealText broadcast by pressing Ctrl+C from the broadcast application console. This terminates the window but will not properly shut down the RealText stream on RealServer.

Developing a Custom RealText Broadcast Application

The RealSystem G2 SDK, which you can download from http://www.real.com/devzone, includes the C++ source code for the RealText broadcast application. Subject to the SDK license agreement, you can customize the broadcast application to do any of the following:

• Compile the RealText broadcast application to run on a different operating system.

• Create a new broadcast application that adds RealText mark-up to a live text stream and sends the data to RealServer.

• Integrate RealText broadcast features into another application.

Closed-Captioning

For closed-captioning, use a device such as TextGrabber from SunBelt Industries (http://www.sunbeltindustries.com). This device supplies text from a TV signal through an RS232 interface. Your customized RealText broadcast application can receive the text, format it with RealText mark-up, and send it to RealServer for broadcast.

Copyright © 1998 RealNetworks
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This file last updated on 12/18/98 at 14:44:50.