When delivering multimedia presentations
across an intranet, most developers think about prerecording
content, digitizing it, and delivering it to the masses in the form
of a multimedia file (such as an MP3). However, 1,000 concurrent
users requesting the same file can put a burden on your
network.

With Windows Media 9 Server, you can serve up
live broadcasts as a multicast. This means that only one stream
serves to the clients that request it. A drawback to live
broadcasts is that they’re difficult to implement. But, with the
Windows Media Encoder 9 Series, this is easier, and the Encoder
is an extensible component that you can script to create a more
specific solution for the broadcaster. In this article, I’ll use
the Windows Media Encoder 9 engine (Encoder) to create a live
multimedia broadcast from a Web page. I’ll also create a client
page to receive the broadcast, as well as custom commands and
captions.

The Encoder is a scriptable component available
as a
free download from Microsoft; it’s also a stand-alone
executable. Encoder will either serve up the live broadcast or push
the load off onto a Windows Media Server. In this example, I’ll
serve the broadcast from my local computer. I’m running Windows XP
Pro with IIS 5.0. The first thing to do is to create a
configuration file, which is an XML file with a .wme extension.

To ease the burden of creating the
configuration file by hand, I start the Encoder and follow the
wizard for creating a live broadcast. The first screen asks for the
video and audio input devices. I have a Web camera and a
microphone, so I select the camera from the drop-down list and use
the default device for the audio. Then it asks whether you want to
push the content to the Windows Media Server or have clients
connect to your computer and pull content.

For my example, I choose Pull. I accept the
defaults for the HTTP port and proceed. On the following screen,
you can set the quality of the audio and video that you wish to
broadcast. (Remember that, the higher the quality, the more
bandwidth it requires.) I choose Live Broadcast for video and Voice
Quality for audio. The next screen asks you if you wish to archive
your broadcast for future use. This is important if you’re doing
executive broadcasts and wish to store the file. However, on my PC,
it would just take up room, so I pass on the archive option.
Finally, follow the screens to the end of the wizard and click
Finish.

Check to make sure that you’re getting a video
feed from your camera, and verify that you’re getting an audio feed
from your microphone by choosing the Audio Panel from the View
menu. You should see an audio level indicator that will move up and
down when you speak. Click on the Properties button from the
toolbar or choose Properties Panel from the View menu. In the
Sources tab, select the “Both Device And File” Source From
option. Check the Script checkbox. (This is important if you use
custom commands.) Save the configuration file and deploy it on your
local site.

Now that you have the configuration file, you
can script the Encoder engine to create a more specific user
experience and avoid having the broadcaster learn how to use the
Encoder; however, the Encoder engine must be on the broadcaster’s
computer.

Here’s the HTML page to accomplish the custom
broadcast:

<html>
<head>
<script language=”JavaScript”>
var g_objEncoder = new ActiveXObject(“WMEncEng.WMEncoder”);
g_objEncoder.Load(“http://localhost/config.wme”);

function start() {
    g_objEncoder.Start();
}
function stop() {
    g_objEncoder.Stop();
}
function sendURL(url) {
    g_objEncoder.SendScript(0, “URL”, url +
“&&frame2”);
}
function sendCmd(cmd) {
    g_objEncoder.SendScript(0, “TEXT”,
cmd);
}
function sendCaption(msg) {
    g_objEncoder.SendScript(0, “CAPTION”,
msg);
}
</script>
</head>
<body>
<button onclick=”start()”>Begin
Broadcast</button>
<button onclick=”stop()”>End
Broadcast</button><br>
<input type=”text” name=”txtURL” id=”txtURL”
size=”50″><br>
<button onclick=”sendURL(txtURL.value)”>Go
URL</button><br>
<textarea id=”txtMsg” rows=”5″ cols=”80″
scroll=”off”></textarea><br>
<button onclick=”sendCaption(txtMsg.value.replace(/\n/g,
‘<br>’))”>Send
 Caption</button><br>
<button onclick=”sendCmd(‘showAlert’)”>Show Alert
Box</button>
</body>
</html>

The reason for doing this as a Web page is
simple. It’s easier to set up a UI quickly in HTML than to create a
custom application. You must allow unsafe ActiveX controls to
initialize and run in order for this page to work, but it shows the
functionality that’s available.

Since all the configuration information is
contained in the configuration file (which you load when the
ActiveX component is created), the broadcaster doesn’t have to go
through the steps of setting up the broadcast environment. All
that’s left is to start and end the broadcast.

The preceding HTML creates a page with two
buttons for starting and stopping the broadcast. There is a text
field for entering a URL and a corresponding button that allows you
to navigate from the client’s browser to the specified URL. There
is a <TEXTAREA> with a corresponding button that allows the
broadcaster to send “captions” to the client, and there’s a button
for sending a command to the client that will be handled by a
JScript block in the client HTML.

Create the client HTML page

Windows Media Player (WMP) can receive
broadcast streams identified in metafiles, which are like catalogs
for WMP. These XML-based files detail the streams associated with
the metafile and reference information about the stream such as the
title, author, and copyright. You must use metafiles in order to
use special commands, give useful information about your stream,
and create playlist entries.

In this example, I specify some information
about my broadcast stream:

<ASX version=”3.0″>
<TITLE>Basic Playlist Demo</TITLE>
    <ENTRY>
        <TITLE>This
is a test.</TITLE>
        <AUTHOR>Phillip
Perkins</AUTHOR>
       
<COPYRIGHT>(c)2004 Phillip Perkins</COPYRIGHT>
        <REF
href=”http://ct.cbsi.com/click?q=44-9nSfIZUaiCjHugYPzmHlc3KmnVOl” />
    </ENTRY>
</ASX>

This code defines the broadcast stream. Note
the <REF> tag; it provides the address of the stream source
for the client. When you set up the Encoder configuration file, you
give your stream a name. The name of my stream was Live, which
you’ll see in the HREF attribute of the <REF> tag.

Here’s the client code:

<html>
<head>
<script for=”player” event=”ScriptCommand(scType, Param)”
language=”JScript”>
alert(scType + “, ” + Param);
</script>
</head>
<body bgcolor=”black”>

<OBJECT id=player style=”LEFT: 0px; TOP: 0px;”
type=application/x-oleobject
 classid=”CLSID:6BF52A52-394A-11d3-B153-00C04F79FAA6″
VIEWASTEXT>
    <PARAM NAME=”URL”
VALUE=”http://localhost/Develop/Media/wm_test.wvx”>
    <PARAM NAME=”rate” VALUE=”1″>
    <PARAM NAME=”balance”
VALUE=”0″>
    <PARAM NAME=”currentPosition”
VALUE=”0″>
    <PARAM NAME=”defaultFrame”
VALUE=””>
    <PARAM NAME=”playCount”
VALUE=”1″>
    <PARAM NAME=”autoStart”
VALUE=”-1″>
    <PARAM NAME=”currentMarker”
VALUE=”0″>
    <PARAM NAME=”invokeURLs”
VALUE=”-1″>
    <PARAM NAME=”baseURL”
VALUE=””>
    <PARAM NAME=”volume”
VALUE=”100″>
    <PARAM NAME=”mute” VALUE=”0″>
    <PARAM NAME=”uiMode”
VALUE=”full”>
    <PARAM NAME=”stretchToFit”
VALUE=”0″>
    <PARAM NAME=”windowlessVideo”
VALUE=”0″>
    <PARAM NAME=”enabled”
VALUE=”0″>
    <PARAM NAME=”enableContextMenu”
VALUE=”0″>
    <PARAM NAME=”fullScreen”
VALUE=”0″>
    <PARAM NAME=”SAMIStyle”
VALUE=””>
    <PARAM NAME=”SAMILang”
VALUE=””>
    <PARAM NAME=”SAMIFilename”
VALUE=””>
    <PARAM NAME=”captioningID”
VALUE=”divCaptions”>
    <PARAM NAME=”enableErrorDialogs”
VALUE=”0″>
</OBJECT>
<br><br>

<div id=”divCaptions” style=”
    width: 95%;
    font-size: 10pt;
    font-family: Verdana;
    color: lightsteelblue;
    height: 100px;
    border: 1px lightsteelblue solid;
    padding: 2px 2px;
“>
</div>

</body>
</html>

The most important part of this page is the WMP
specified by the <OBJECT> tag. There is a number of
<PARAM>s associated with this object, but the two most
important ones (for my purposes) are the URL parameter and the
captioningID parameter. The URL is the address of the metafile, and
the captioningID is the ID of the <DIV> element for
displaying any captions—divCaptions on this page.

Also note the <SCRIPT> in the page. This
script handles the ScriptCommand event of the WMP. When you send a
command with the stream, this command will deliver to this event
handler. In my script, I simply create an alert box that displays
the two parameters passed to the handler. You can use this
functionality to create other actions that will occur when the
broadcaster sends a special command, such as filling out form data
on an associated form.

In my previous example, I gave the broadcaster
the ability to send a URL command to the client. At the end of the
URL, I concatenated the string “&&frame2”. This tells WMP
what frame to target the URL. This can come in handy if you have a
Web presentation, and you want to progress through a series of
exported slides. You’d include this Web page in one frame and put
the “slides” in the adjoining frame.

Windows Media 9 Services makes it extremely
easy to create custom multimedia streams and broadcasts with little
effort. Another benefit is the cost—the
Encoder is a free download, and Windows Media 9 Services (the
server component) is included as an option in Windows 2003 Server.
You can also add Windows Media 9 Services to Windows 2000
Server.

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