Intranet Handbook: Multimedia with a SMIL, 6/29/98

Error 404--Not Found

From RFC 2068 Hypertext Transfer Protocol -- HTTP/1.1:

10.4.5 404 Not Found

The server has not found anything matching the Request-URI. No indication is given of whether the condition is temporary or permanent.

If the server does not wish to make this information available to the client, the status code 403 (Forbidden) can be used instead. The 410 (Gone) status code SHOULD be used if the server knows, through some internally configurable mechanism, that an old resource is permanently unavailable and has no forwarding address.

Multimedia with a SMIL

By Mark Gibbs
Network World, 6/29/98

Your CEO has a flash of genius regarding the intranet: He wants to post a slideshow that employees can look at while listening to him explain his new diversification strategy.

That's great, you think. You've wanted to create a snazzy multimedia application for the intranet, and synchronizing an audio track with images in the slideshow will satisfy that itch.

But your euphoria will fade, and fast, because you'll quickly find there's a major problem with creating multimedia Web presentations: It's impossible to synchronize when and where on the screen the different media are presented. And without synchronization, Web content lacks the dynamism that makes for a powerful information delivery mechanism.

Today, delivering a slideshow with synchronized audio means you have to use complex JavaScript, Java applets or ActiveX kludges. Portability among operating systems is out of the question.

But vendors and standards bodies have been pursuing a way to deliver synchronized multimedia applications on the Web. The most advanced approach is Synchronized Multimedia Integration Language (SMIL). Pronounced "smile," SMIL allows for flexible integration of multiple media streams.

The World Wide Web Consortium (W3C) has signed off on SMIL as a Proposed Recommendation and is testing early proof-of-concept implementations. An even more encouraging sign is that SMIL has gathered good industry support since becoming a working draft last November. The support comes from a number of influential organizations, including Lucent/Bell Labs, RealNetworks, Inc., Microsoft Corp., Netscape Communications Corp., Philips Electronics N.V. and Digital Equipment Corp.

The proposed SMIL standard defines how a multimedia Web broadcast is specified in a single file. This .smi file is a simple text file that you can create and modify with any text editor. The file's content is a relative of HTML.

One of SMIL's great appeals is simplicity. The specification uses only six tags, and you can harness most of SMIL's power by mastering just two of them - <parallel> and <sequential>. These define when to play media items.

The <sequential> tag is the default for untagged media items. For example, the following SMIL file will play the referenced sound files in sequence:

The <smil> tag simply declares that the file is a SMIL specification. The header uses the standard HTML meta tags to define presentation attributes, which are global definitions unless overridden.

Overriding is easy. For example, if you need to cite a different author, you can override the attributes with a local definition. Overriding can be applied to any attribute, as shown here:

SMIL can use any multimedia streaming protocol but the SMIL documentation references the Real Time Streaming Protocol (RTSP) because it is the most developed. The Internet Engineering Task Force is considering RTSP, specified in RFC 2326, as an Internet Draft.

More media
To play media items in parallel, you would use the <parallel> or <par> tag. The following shows a file for playing an audio track along with a video and text:

You also can define what part of an item is played, and when. Writing <audio src="rtsp://www.gibbs. com/introtune.ra" begin="6s" clip-begin="1.4s" clip-end= "15.0s"/> would delay the audio for 6 seconds, then have it play from 1.4 seconds into the data until 15 seconds into the data.

SMIL's <layout> tag specifies exactly where items will appear on the rendered Web page. This tag defines regions and attributes for the media items displayed. The <root-layout> tag specifies the entire display region size and color and then specific areas inside that are defined by name.

For example:

</smil>
<head>
<layout>
<root-layout background color="grey"
height="400" width="300"/>
<region id="region1" top="5" left="5"
height="180" width="240"/>
<region id="region2"top="200" left="5"
height="25" width="280"/>
</layout>
</head>
<body>
<seq>
<par>
<video src="intro.rm" region="region1"/>
<textstream src="banner.rt" region="region2"/>
<audio src="intro.ra"/>
</par>
<par>
<video src="main1.rm" region="region1"/>
<video src="main2. rm" region="region2"/>
<audio src="main.ra"/>
</par>
</seq>
</body>
</smil>

In the "head" section, I've defined two regions inside the main "root-layout" region. The body section assigns the playing of the media in the first <par> block and then those in the second <par> block. Note that the use of the regions can be changed as required - the first <par> block plays text in region2 while the second <par> block uses that region for video.

Another SMIL feature is the ability to specify different aspects of the connection quality and environment. This allows the server or browser to select media with the appropriate resolutions for the available bandwidth.

SMIL's future looks bright. The W3C is testing early SMIL interpreters, and RealNetworks has incorporated SMIL in its latest product, RealSystem G2 (see graphic). This is a safe starting point for experiments with synchronized multimedia presentations.

Feedback | Network World, Inc. | Sponsor Index
Marketplace Index | How to Advertise | Copyright

Back to the IntraNet index page

The World Wide Web Consortium Audio, Video, and Synchronized Multimedia page

Synchronized Multimedia Integration Language (SMIL) 1.0 Specification

RealNetworks, Inc. SMIL Resource Page

Songline Studios' WebReview
Streaming Media to Make You SMIL:

SMIL Resources P>