Common Audio Formats

Here are some common formats you might encounter, or consider using for audio on your website. Many of these are, of course, older than the web itself.

AIFF (audio interchange file format)

Widely used on the Mac and the web.
Extension: .aiff, .aif
MIME type: audio/aiff, audio/x-aiff
Comes in uncompressed and (many) compressed flavors. Uncompressed AIFF is widely supported


Widely used on PCs and the web
Extension: .wav
MIME type: audio/wav, audio/x-wav
Comes in uncompressed and (many) compressed flavors. Uncompressed WAV is widely supported.


NeXT/Sun file format. Widely used on Unix systems (and Java).
Extension: .snd, .au
MIME type: audio/basic
Supports uncompressed 8-bit and 16-bit, and compressed 8-bit and 16-bit. Many players support only 8-bit uncompressed.

MP3 (MPEG-1 Layer 3)

Motion Picture Experts Group compression standard. Very popular web format.
Extension: .mp3, .mpu
MIME type: application/mp3, audio/x-mpegurl
High quality but not lossless compression (typically 10:1). Insufficient compression to stream over 56k or ISDN dialup connections. Many free MP3 players are available for all platforms, but not many support streaming. There are also some freeware or shareware encoders for converting soundfiles into MP3 format. On the Mac, I've used Johan Lindvall's free MP3 encoder.


Proprietary format from RealNetworks. Highly compressed.
Extension: .ra, .ram, .rm
MIME type: audio/x-pn-realaudio, audio/x-pn-realaudio-plugin
Can stream reasonably well over dialup connections. Supported only by RealPlayer (free download from, available for most platforms)

MIDI (Musical Instruments Digital Interface)

Originally control protocol for digital synthesizers. Encodes musical events such as note-on/off, pitch etc, not digital audio.
Extension: .mid, .kar
MIME type: audio/midi, audio.x-midi
MIDI players generally use .mid files to drive software synthesizers to produce audio. .kar is a karaoke format which is a MIDI track with a synchronized text track. Widely supported.


Contains MIDI data with samples for each voice.
Extension: .mod