6.4.1. Broadcasting through firewalls

1. Multicast IP

2. UDP

3. TCP

4. HTTP

The process works as follows:

1. First, the user, either via the plug-in or a .ram file, is directed to the RealServer via a TCP connection from within the firewall to the RealServer.

2. Next, the server, via a TCP connection, sends the stream information (header, if you will) to the player.

3. Third, the server sends the stream to the client via the most efficient mechanism, as noted above. If no data is received after a specific amount of time, usually two seconds for the RealPlayer, the player notifies the server and the server streams the content via the next most efficient protocol. This continues until there is no connectivity even via HTTP. The player then gives an error message and stops trying.

If you need to stream audio from behind a firewall to the public Internet, you have two options:

Broadcasting to a corporate LAN (Intranets)   For broadcasting audio over an Intranet instead of the public Internet, you need to take extra steps to prevent network congestion. Nick DelRegno, engineer for MCI Enterprise Information Systems, outlines the best method for broadcasting over an Intranet:   To broadcast RealAudio or RealVideo, configure the LAN/MAN/WAN for IP Multicast. By using IP Multicast for the live broadcasts, you can hit every employee with minimal impact on the network. With the advent of IP Multicast-aware Ethernet Switches, you can even control the impact of Multicast on your flat LAN segments.   MCI Enterprise Information Systems has had very good success with multicasting 20 Kbps to 300Kbp RealAudio and RealVideo streams across their network. The only problems encountered have been on busy LAN segments and on Token Ring LANs.   RealNetworks also supports unicast (UDP, TCP, and HTTP) streaming so that anyone on a non-multicast-enabled portion of the network, such as dialup, can access the content via a unicast connection. With the deployment of Resource Reservation protocols and IP Quality of Service, busy LANs should become less of an issue.   MCI Enterprise Information Systems has deployed several servers to handle the load, one with redundancy for live events and several others to replicate content and distribute the load for archived content. "We don't do any splitting because of the nature of our network; however, for LANs connected by thin pipes, this is a nice option. Our servers are located centrally within our Intranet so that the encoder can sit anywhere, even in very remote locations connected via ISDN dialup."   For security, Nick set up specific multicast address ranges, which get blocked at MCI's boundary routers. He also set relatively low TimeToLive (TTL) settings on MCI's multicasts. This helps prevent multicast leakage onto the public Internet, yet allows them to multicast globally.

6.4.2. Creating custom player controls

• Bypass the player interface so that your audio content will begin playing immediately when a user enters a web page.

• Build the player interface directly into your web page.

• Use the standalone RealPlayer controls.

Figure 6-8. The Radio CounterCulture page with embedded RealPlayer controls

The drawback to using embedded controls is that the audio will stop playback when a user leaves the site. Many listeners prefer to listen to audio while they view other web sites. If you want to cater to the "listen while they surf" crowd, you will have to hide the player by embedding the player in a zero height or width frame or by simply not embedding the player in the web page. By hiding the player in a zero height or width frame, you can continue to play the content until the user manually enters a new URL or until a _top or _parent frame target is used.

6.4.3. Indexing RealMedia clips: creating a table of contents

For example, a one-hour music CD or instructional video could be indexed by utilizing the start and stop tags within a .ram or .rpm file. To create a .ram file for indexing a RealMedia clip, simply add the start and stop parameters to the URL in your metafile as shown below:

pnm://servername.com/yourfile.rm?start=2:23.4&end=2:59.2

Most of the time, these files are preset when the clips are published, but if you enter your start and stop information in a database, you can generate the .ram file on the fly. By doing this, you can place a table of contents on the page with each topic pointing to a .ram file with the appropriate start and stop information. This technique gives you the ability to use one file to provide full-length playback or random (shuffle) play.

In the head part of your HTML document, insert the <script> tag with the following function:

<script language="JavaScript">
 function startClip(Clip,Start,End,Title,Author,Copyright) {
// uncomment next two lines or set server in HREF below
// server = 'pnm://yourRealServer.com/'
// Clip = server + Clip;
  if(Start == null) Start = '0';
  Clip = Clip + "?start=" + '"' + Start + '"';
  if(End != null) {
    Clip = Clip + "&end=" + '"' + End + '"';
  }
  if(Title != null) {
    Clip = Clip + "&title=" + '"' + Title + '"';
  }
  if(Author != null) {
    Clip = Clip + "&author=" + '"' + Author + '"';
  }
  if(Copyright != null) {
    Clip = Clip + "&copyright=" + '"' + Copyright + '"';
  }
// uncomment following line for testing: 
// alert("URL: " + Clip);
  if (navigator.appName == "Netscape") {
    document.VideoObjName.DoStop();
    document.VideoObjName.SetSource(Clip);
    document.VideoObjName.DoPlayPause();
    } else {
    VideoObjName.DoStop();
    VideoObjName.Source= Clip;
    VideoObjName.DoPlayPause();
  }
 }
 </script>

This function pastes together the necessary URL to play a clip, stops the previous clip (if any), sets the source of the plug-in to the new clip, and starts playing at the indicated start time. The server location is included in the call to the function. You can also hardcode the function itself at the indicated location within the function. The only required parameter is the clipname. Use 'null' (notice the single quotes) if there is no value for an argument. clipnameincludes the complete address and filename.

At the minimum, the plug-in should look something like this:

<embed name="VideoObjName" type="audio/x-pn-realaudio-plugin"
width="176" height="144" controls="ImageWindow">

This code will work in both IE 3.0 and greater and Netscape 2.0 and greater. It is strongly recommended that you not put the <embed> tag within a table for cross-platform compatibility.

When you link to the content, call the startClip function, as follows:

<br> <A HREF="JavaScript:startClip( 'pnm://your.realserver.com/
glasr56.rm', '00:00:27.0', '00:00:54.1', null, null, null)"> TimeN 
</A>

Or you can use an image and call JavaScript using the onClick function, as follows:

<IMG SRC="button.jpg" onClick=startClip(video1.rm, 00:02:37.0,
    00:03:34.1, null, null, null)>

6.4.4. Creating RealFlash content

Figure 6-9. The Club Internet RealFlash motor scooter tour of Montmartre in Paris with a RealVideo window embedded in a Flash animation screen

To create your own RealFlash content, build a multimedia presentation in Macromedia Flash, and then export the animation as a Shockwave movie file and the streaming audio portion as a separate AVI video file. Use the RealNetworks tools to convert the Flash video file into the RealAudio format. Your final RealFlash presentation will consist of two files:

To create a RealAudio file, follow these steps:

1. With the same Flash file still open, select File Export Movie.

2. In the dialog box, choose AVI as the file type. Make sure to use the .avi file extension in your filename.

3. In the Export Windows AVI dialog box, select dimension 32 x 32 regardless of the movie's true dimensions. Click OK to create the AVI file. This minimizes file size and creation time.

4. Open the RealEncoder or RealPublisher and choose File Open Session.

5. On the Source panel, click File and add your AVI file to the list box. On the Destination panel, click RealMedia and specify an output filename with the .rm extension. Click OK.

6. In the Templates panel, click Advanced and deselect video. Then select an audio codec. This tells the encoder to save only the synchronized audio portion of the AVI file.

7. Enter a template name and click Save. Then click Close.

8. In the Templates panel, click Start to create your audio file, and you are ready to go with RealFlash.

Once you have created the .swf and .rm files necessary for a RealFlash presentation using the RealSystem 5.0, your web pages will need to link to the appropriate metafile, which in turn points to the DNS name or IP address of the computer on which your RealServer and RealMedia files are located.

pnm://www.server1.com/hello.rm+hello.swf

pnm://server.domain.com/realaudio.rm+realflash.swf

6.4.5. Creating synchronized RealAudio presentations with RealSystem 5.0

If you are using RealSystem 5.0, there are two basic options for creating real-time multimedia presentations with fast forward, rewind, and pause controls:

At an All-Star Game Fan Fest, News Corp. hosted a booth to educate people about its media presence on the Web. News Corp. developed a RealAudio-guided tour for large screen video display to promote their various web site properties such as TV Guide Entertainment Network. RealAudio, combined with the Cevents command-line tool included in the RealServer package, provided a simple solution.

By simply adding an extra Cevent text file containing all the URL links and their time specifications into the same directory as the .ra file, Dadekian quickly generated an audio-visual guided tour.

When a user accesses the guided tour, the server goes to play the tour.ra file but notices there is a tour.rae file in the same folder. As the RealAudio Event file plays, it triggers the web browser to display web pages at the proper times.

6.4.6. Database management and tracking of RealAudio content

A database can also be useful for implementing a variety of interesting applications besides simply organizing your content. For example, with Cold Fusion from Allaire you can select a particular .ram file in a tree and then execute it according to the day of the week or a particular category selection made by a user. Further, MCI's Nick DelRegno reports that their database is tied to their live scheduling system to dynamically return live events upon request and generate the appropriate .ram or .rpm file for the user.

Larry Bouthillier, head of multimedia production at Harvard Business School, recommends building a database of all the metadata of your content, including title, filename and path, servername, start time, end time, and so on. A Java servlet can then be used to piece together a .ram file-type string and return it to the browser with the appropriate MIME type header.

One good thing about having all the metadata in a database is that you can make a web form that enters new entries into the database. According to Bouthillier, "Creating a new video clip is as easy as filling in the filename, start and end times, and saving it to the database. You also have the beginnings of a primitive online video editing system."

For more on Java servlets, see Java Servlet Programming by Jason Hunter (O'Reilly, 1998).

6.4.7. Load balancing

#!/usr/bin/perl
# usage: 
http://www.webserver.com/cgi-bin/load?anything.rm
#@ip = ( 'server1', 'server2', 'server2', 'server2', 'server3' );
#$content = $ENV{'QUERY_STRING'};
srand($$ + time);
$count = int(rand($#ip + 1));
print "Content-type: audio/x-pn-realaudio\n\n";
print "pnm://$ip[$count]/$content\n";

To get the Perl script up and working, follow these steps:

In the code above, the ip array contains five elements:

ip[1] = server1
ip[2] = server2
ip[3] = server2
ip[4] = server2
ip[5] = server3

Using this list, server1 will get 20% of the load, server2 will get 60%, and server3 will get 20%. By adding multiple entries, you can obtain any prescribed balance.

You can easily modify this Perl script to randomly select RealAudio clips. For example, if you want visitors to your site to be able to listen to a different audio file each time they visit a particular page, you could modify the Perl script to randomly call 1 of 10 files.