mp3 A format on the Web for distributing CD-quality music. A 1 Mb files is equal to about one minute of music. File Type:Binary. This type of file requires an MP3 player, which is available for both Macintosh and Windows.
m4a (mp4, m4a, aac): MPEG-4 is used to store digital audio and digital video streams. It is based on Apple's Quicktime. File sizes are smaller than mp3.
m4a to mp3: In iTunes prefs, set Import Using to MP3, then choose Convert Selection to MP3 from the Advanced menu.
File Format Conversion: You will want to present your sound files in the format that you believe most listeners will wish to hear. Most Macintosh programs save files as aif files (Audio Interchange) while most Windows based machines save them as wav (wave) files. On the web, however, it is generally best to save sound as Real audio (ra, ram) or MPEG (mpg, mp3) files. To convert, you will need to use a utility.
aif - Audio Interchange File Format; Common sound format found on the Web. File Type: Binary, Although it is a Macintosh format, it can be used on other platforms as well. It requires the same programs as .au to play.
au - Sun Audio; The most common sound format found on the Web. File Type: Binary, Macs need SoundApp to play this type of file; PCs can use Waveform
wav - Windows Wave; The native sound format for Windows. File Type: Binary. On the Mac, you can use Sound App to play .wav files. For the PC, use aveform Hold and Modify or Goldwave to play these files. There's also a good program called Win Play! (wplnyxx.zip) that will play it, as well as other popular formats.
mid - MIDI: Musical Instrument Digital Interface.
ra - RealAudio. RealAudio allows you to play sounds in real-time. File Type: Binary. This file type requires a Real Player, which is available for both Macintosh and Windows.
swa - ShockWave (MP3)
sd2 - Sound Designer