Standard web audio formats include AU, MP3, MIDI, WAV, and AIFF. Other popular propriatary formats include Flash, RealAudio, QuickTime, Windows Media, and Shockwave. Proprietary player applications can often play several standard formats and, in some cases, they can play propriatary formats from other companies.
AU - an audio format developed by Sun Microsystems. It is the original internet audio format and, therefore, the most compatible. Since the format is limited to 8-bit samples, it is not the best choice for delivery of music ... even when using µ-Law or a-Law compression to improve performance.
WAV and AIFF - also widely compatible formats, capable of the highest quality of sound reproduction. The WAV format was established originally on the PC platform, while AIFF was a Mac format. Most recent player applications that can play either format, are capable of playing both. Though these formats provide the hi-quality sound, there is a substantial "hit" due to the size of these files (e.g., a 1-minute CD-quality musical excerpt (16-bit, 44.1 KHz sample rate, stereo) results in a file that is over 10 MB in size. There is little reason to use these formats on the web anymore because compressed formats such as MP3 provide a viable alternative, reducing the file size substantially while still - for typical purposes - providing acceptable sound quality.
MP3 - recently gained a great deal of popularity due to its relatively high-quality audio (approaching CD quality), while reducing file size by a factor of 10 or more. Encoding is easy and inexpensive ... there are many free encoders available and the capability of creating MPG files is included in many sound editors. Distribution is simple via HTTP, FTP, or on data CDs.
RealAudio - designed primarily for streaming media, RealMedia provides the possibility of creating simple, synchronized media presentations, e.g., slide shows, audio with moving text, captions, and pictures. In order to access these files, the designer must create a RAM file (a text file that contains the absolute URL of the RealAudio file on the RealServer). The HTML link must be made to the RAM file, rather than the RealAudio file. Using RealProducer, it is easy and intuitive to transform CD tracks or digital audio files to RealAudio format. SureStream technology allows the creation of a single file that allows users to receive the highest possible sound quality on the basis of their connection speed. In addition, it is possible to use "start" and "end" parameters to begin and end playback at various points within the RealAudio file.
QuickTime - though this format can be used for audio files, its real strength is in the ability to create interactive multimedia files, including sound & animation. The files can be accessed either via HTTP using "Fast Start" technology, allowing the file to begin playback prior to completing the process of downloading the file. QuickTime can also be streamed by saving the QuickTime file as a "hinted" movie and creating a "Reference Movie" that points to the the hinted file which must reside on a QuickTime server. The HTML link must be made to the Reference Movie, rather than the hinted movie.
Flash & Shockwave - Flash is a popular playback standard and a relatively easy-to-use multimedia authoring environment. It provides an excellent means of producing button rollovers, transitions, sound effects, loops, and audio synced to animation. Files created in Macromedia's Director can be saved as Shockwave movies for distribution over the web. Though the program has a fairly steep learning curve, it is capable of creating extremely complex interactive multimedia files. Director's scripting language (Lingo) is a powerful tool for authoring files in both its own native format and for distribution over the internet via Shockwave.
MIDI - the advantage of MIDI files is that the file size (even for long musical pieces) are very small. However, unless the user is using a MIDI-enabled player like QuickTime or Beatnik, the sound is produced using whatever MIDI sound set is installed on the computer accessing the sound file. This can result in widely varying results.
Beatnik - the Rich Music Format (RMF) proprietary format is a hybrid of MIDI data and sample-based sound sets (similar to the QuickTime Musical Instruments set). RMF yields very small files and high interactivity, via JavaScript. Using its set of instrument sounds, the designer can be assured that all users will receive consistent playback across platforms and/or browsers. The process of adding such interactivity to a web site is called "sonification."
Liquid Audio - matches high-quality compressoin with flexible secruity. This format is oriented more toward commerce and controlled music distribution than interactivity, providing an end-to-end solution for editing, mastering, purchasing, distributing, and playing high-quality audio files over the internet. It is designed to track sales, keep licensing and copyright information in place, and provide advanced security features, including digital watermarking and encryption. Allows musicians to easily set conditions for how a file can be used (e.g., no limitations, file can be disabled after a period of time, etc.).
Koan - yields small, highly interactive files, though the format is geared primarily toward generative composition.
Ogg Vorbis - an open-source, free-license alternative to MP3.
RMF and Koan are examples of structured formats, in which descriptive information about the data remains visible to outside applications that can act on the data in real time. The difference between structured and unstructured formats (like WAV and MP3) is like the difference between a fax and an email. A fax is fixed on the page .... you can't do much to change it beyond physically cutting up the paper. An email remains infinitely editable. Some formats (like QuickTime) can incorporate unstructured data and some structured data, e.g., MIDI and animation sprites. Generally, structured data appears to be teh trend of the future. MPEG-4 aims to be the ultraformat, offering a structured approach to every form of media ... all in the same file.