Chapter 4: RealPix Broadcasting

The RealPix broadcast application connects to RealServer G2 and polls a specified directory every second for an updated image file, which can be in JPEG or static GIF format. When it finds an updated image file, it sends the file to RealServer, which broadcasts the file to the connected RealPlayers. New files replace old files with a transition that alternates between a fade-in and a "push" wipe transition.

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

RealPix Broadcast Application

You can broadcast RealPix 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 RealPix Broadcast Application".

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

Installing the RealPix Broadcast Application

The RealPix broadcast application comprises the exlvpix.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 a RealPix broadcast machine. You can use the RealServer G2 machine or any Windows 32-bit machine with a network connection to RealServer G2. RealPix broadcast requires minimal system resources, but RealNetworks recommends using a Pentium 133 MHz or faster processor with at least 32 Megabytes of memory.

Creating a Broadcast RealPix Clip

Create RealPix broadcast images in JPEG or static GIF format. You set RealPix window attributes such as width and height when you start the broadcast application. RealServer sends these attributes to each RealPlayer when it connects to the broadcast. The broadcast images then scale to the window size when received by RealPlayer, maintaining their height-to-width aspect ratios.

	Additional Information
	For more on aspect ratios, see "Controlling Image Aspect".

Setting the Broadcast URL

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

<a href="http://realserver.company.com/ramgen/encoder/media/slides.rp">...</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 and names 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 RealPix broadcast:

<textstream src="rtsp://realserver.company.com/encoder/media/slides.rp"/>

Using SMIL, you can embed a RealPix broadcast in a multiclip presentation. You might have a RealAudio narration and a RealPix region for broadcast images, for example. The SMIL file uses the broadcast URL for RealPix and a standard URL for the on-demand RealAudio clip. Each person who views the presentation hears the audio from its normal beginning, but joins the RealPix broadcast in progress.

	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/index.html.

Starting the RealPix Broadcast Application

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

c:\RealPix> exlvtext.exe server port filename imgname width height bitrate

The following table explains the parameters you enter on the command line. Enter all values without quotation marks.

Moving a RealPix File to the Broadcast Directory

Once started, the broadcast application checks the designated directory every second for an updated image file. You can place a new file in the directory manually or use any automated method. All files must use the same image file name specified during application start-up.

Make sure that the frequency with which you broadcast images does not exceed your broadcast bit rate. If a broadcast image is 35 Kilobytes (280 Kilobits) and your broadcast rate is 10 Kbps, for example, RealServer needs 28 seconds to broadcast that image.

	Additional Information
	For more on bandwidth, read "Bandwidth Usage" starting.

Stopping the Broadcast Application

To stop the RealPix broadcast stream, type a lowercase q at the RealPix command console. This causes RealServer to terminate the broadcast stream. It also shuts down the application console window on the RealPix broadcast machine.

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

Developing a Custom RealPix Broadcast Application

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

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

• Modify the broadcast application with new features.

• Integrate RealPix broadcast features into another application.

Copyright © 1998 RealNetworks
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This file last updated on 12/18/98 at 17:28:48.