5.4 Background Audio

There is one other form of inline multimedia generally available to web surfers — audio. Most browsers treat audio multimedia as separate documents, downloaded and displayed by special helper applications, applets, or plug-ins. Internet Explorer, on the other hand, contains a built-in sound decoder and supports a special tag (<bgsound>) that lets you integrate with your document an audio file that plays in the background as a soundtrack for your page. [Section 12.1] [Section 12.2]

We applaud the developers of Internet Explorer for providing a mechanism that more cleanly integrates audio into HTML and XHTML documents. The possibilities with audio are very enticing, but at the same time, we caution authors that Internet Explorer's special tags and attributes for audio don't work with other browsers, and whether this is the method that the majority of browsers will eventually support is not at all assured.

5.4.1 The <bgsound> Tag

Use the <bgsound> tag to play a soundtrack in the background. This tag is for Internet Explorer documents only. Other browsers ignore the tag. It downloads and plays an audio file when the host document is first downloaded by the user and displayed. The background sound file also will replay whenever the user refreshes the browser display.

<bgsound> Function Plays a soundtrack in the document's background Attributes loop, src End tag None in HTML Contains Nothing Used in body_content

5.4.1.1 The src attribute

The src attribute is required for the <bgsound> tag. Its value references the URL for the related sound file. For example, when Internet Explorer users first download a document containing the tag:

<bgsound src="audio/welcome.wav">

they will hear the welcome.wav audio file — perhaps an inviting message — play once through their computers' sound systems.

Currently, Internet Explorer can handle three different sound format files: wav, the native format for PCs; au, the native format for most Unix workstations; and MIDI, a universal music-encoding scheme (see also Table 5-1).

Table 5-1. Common multimedia formats and respective filename extensions

Format	Type	Extension	Platform of origin
GIF	Image	gif	Any
JPEG	Image	jpg, jpeg, jpe	Any
XBM	Image	xbm	Unix
TIFF	Image	tif, tiff	Any
PICT	Image	pic, pict	Any
Rasterfile	Image	ras	Sun
PNG	Image	png	Any
MPEG	Movie	mpg, mpeg	Any
AVI	Movie	avi	Microsoft
QuickTime	Movie	qt, mov	Apple
AU	Audio	au, snd	Sun
WAV	Audio	wav	Microsoft
AIFF	Audio	aif, aiff	Apple
MIDI	Audio	midi, mid	Any
PostScript	Document	ps, eps, ai	Any
Acrobat	Document	pdf	Any

5.4.1.2 The loop attribute

As with Internet Explorer's inline movies, the loop attribute for the browser's <bgsound> tag lets you replay a background soundtrack a certain number of times (or indefinitely), at least until the user moves on to another page or quits the browser.

The value of the loop attribute is the integer number of times to replay the audio file, or infinite, which makes the soundtrack repeat endlessly.

For example:

<bgsound src="audio/tadum.wav" loop=10>

repeats the ta-dum soundtrack 10 times, whereas:

<bgsound src="audio/noise.wav" loop=infinite>

continuously plays the noise soundtrack.

5.4.2 Alternative Audio Support

There are other ways to include audio in your documents, using more general mechanisms that support other embedded media as well. The most common alternative to the <bgsound> tag is the <embed> tag, originally implemented by Netscape and supplanted by the <object> tag in the HTML 4 and XHTML standards. Take a look in Chapter 12 for details.

Ultimately, all background audio, including spoken document content, should be handled using the various audio extensions defined in the Cascading Style Sheets 2 (CSS2) standard. While we cover all of these extensions in Chapter 8, they are not yet supported by any browser. When such support becomes widely available, all of these early audio extensions will go the way of the <blink> and <isindex> tags, early specialized tags deprecated in favor of more generalized and powerful features.