Many audio formats can be used to embed sound in Web pages, but the following are the most popular ones: WAVE, AU, and MIDI. WAVE (Waveform Audio File Format) is stored in files with a ".wav" extension, and was invented by Microsoft for the Windows platform. AU (Audio File Format) is stored in files with a ".au" extension, and was invented by Apple for the Macintosh platform. Both the WAVE an AU formats store "recorded" sounds and tend to occupy a lot of space. A one-second sound track may require approximately 50 kilobytes of disk space, depending on its quality.

The MIDI format is entirely different. If we compare the various audio formats to well-known graphic representations, AU and WAVE relate to bitmap graphics, while MIDI resembles vector art. The MIDI format actually includes commands, specifying the note to play next and for how long. A MIDI command looks like this: "play the high D for 0.25 seconds." Due to its command structure, MIDI format is relatively compact. The down side of MIDI format is that it is quite difficult to compose a music with a command sequence.

The only problem with MIDI files is that some servers are not yet familiar with it and tend to send wrong identification information to the browser. When a server sends a file to the browser (after the browser had requested the file), it first identifies the type of data being sent via the MIME (Multipart Internet Mail Extension -- see later in this column) header. For instance, plain HTML text is recognized by the "text/html" MIME type. Although MIDI files are stored with ".mid" or ".midi" extensions, some servers still incorrectly identify them. The MIME type for a MIDI file should be "audio/midi," and the best way to solve this problem (if it exists) is to send a note to your server administrator. Note that the server should also support the "audio/x-midi" MIME type.