336 Chapter 19 – Audio on the WebNonstreaming (Static) Audio
Web Design in a Nutshell, eMatter EditionFile Formats
A multitude of audio file formats exist for use on computers today. The following
list represents just those that are widely used on the Web because of their cross-
platform and cross-browser support.
WAVE (.wav)
The Waveform Audio File Format was originally developed as the standard
audio format for the Microsoft Windows operating system, however, it is now
supported on the Macintosh as well. WAVE files can support arbitrary
sampling rates and bit depths, although 8 KHz and 11.025 KHz at 8- or 16-bit
are most common. Its performance is similar to AIFF.
AIFF (.aif, .aiff)
The Audio Interchange File Format was developed as the standard audio
format for the Macintosh platform, however, it is now supported by Windows
and other platforms. It can support up to six channels and arbitrary sampling
rates and bit depths, with 8 KHz and 11.127 KHz at 8-, 16- and 32-bits being
the most common. Its performance is similar to WAVE.
μ-LAW (.au)
-Law (pronouncedmyoo-law) is the Unix standard audio format..aufiles
support mono or stereo channels, variable bit depths, and the following
sampling rates: 8.013, 22.05, and 44.1 KHz. Its popularity as an Internet file
format is waning because Unix platforms have become a small minority on
the Web and because other cross-platform audio formats offer better sound
quality.
MPEG (.mpa, .mp2, .mp3)
MPEG is actually a family of multimedia standards created by the Moving
Picture Experts Group. It supports three types of information: video, audio,
and streaming (which is synchronized video and audio). MPEGs can also be
used as a streaming audio format, as in Xing’s Streamworks technology.
MPEG audio files maintain pristine sound quality at compression rates as high
as 10:1. They do this by using a lossy compression scheme that strips out
sounds that are not discernible to the human ear.
There are a number of MPEG standards: MPEG-1 was originally developed for
video transfer at VHS quality; MPEG-2 is a higher-quality standard that was
developed for television broadcast; other MPEG specs that address other
needs (such as MPEG-4 and -7) are currently in development. MPEGs can be
compressed using one of three schemes: Layer-I, -II, or -III. The complexity of
the coding (and therefore the processor power needed to encode and
decode) increases at each level. Due to this complexity, you need special
encoding tools to produce MPEG audio files.
On the Web, the most popular MPEG formats are MPEG-2, using compres-
sion Layers II and III (with the suffixes.mp2and.mp3, respectively). The
suffix.mpa denotes a file that is audio only.
Netscape Navigator and Internet Explorer may support MPEG audio via the
use of the QuickTime Plug-in. Or you could configure your browser to use