Section 5.4. Background Audio

5.4. Background Audio

One other form of inline multimedia is generally available to web surfersaudio. Most browsers treat audio multimedia as separate documents, downloaded and displayed by special helper applications, applets, or plug-ins. Internet Explorer and Opera, on the other hand, contain built-in sound decoders and support 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. [Applets and Objects, 12.1] [Embedded Content, 12.2]

We applaud the developers of Internet Explorer and Opera 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 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 and Opera documents only. Other browsers ignore the tag. It downloads and plays an audio file when the user first downloads and displays the host document. 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 or Opera users first download a document containing the tag:

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

they will hear the welcome.wav audio fileperhaps an inviting messageplay once through their computers' sound systems.

Currently, <bgsound> can handle several different sound format files, including .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
Graphics Interchange Format	Image	gif	Any
Joint Photographic Experts Group	Image	jpg, jpeg, jpe	Any
X Bit Map	Image	xbm	Unix
Tagged Image File Format	Image	tif, tiff	Any
PICT	Image	pic, pict	Apple
Rasterfile	Image	ras	Sun
Portable Network Graphics	Image	png	Any
Moving Pictures Expert Group	Movie	mpg, mpeg	Any
Audio Video Interleave	Movie	avi	Microsoft
QuickTime	Movie	qt, mov	Apple
Windows Media Video	Movie	wmv	Microsoft
Shockwave	Movie	dvr	Macromedia
Real Video	Movie	ra, rm, ram	Real Networks
DivX	Movie	div, divx, tix, mp4	DivX
AU	Audio	au, snd	Sun
Waveform Audio	Audio	wav	Microsoft
Audio Interchange File Format	Audio	aif, aiff	Apple
Musical Instrument Digital Interface	Audio	midi, mid	Any
PostScript	Document	ps, eps, ai	Any
Acrobat	Document	pdf	Any

5.4.1.2. The loop attribute

As with 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, you should handle all background audio, including spoken (aural) document content, using the various audio extensions defined in a CSS standard. While we cover the speech synthesis-related 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.