Plug-ins - When Netscape programmers were working on early versions of the browser, they faced the problem that multimedia files lacked any reliable standard. Rather than try to build Netscape to handle all the available multimedia formats, they decided to use plug-ins to handle multimedia. Audio and video files need some sort of helper application to be installed by the end users.

MIDI - musical instrument digital interface, a standard adopted by the electronic music industry for controlling devices, such as synthesizers and sound cards, that emit music. At minimum, a MIDI representation of a sound includes values for the note's pitch, length, and volume. It can also include additional characteristics, such as attack and delay time.

The MIDI standard is supported by most synthesizers, so sounds created on one synthesizer can be played and manipulated on another synthesizer. Computers that have a MIDI interface can record sounds created by a synthesizer and then manipulate the data to produce new sounds. For example, you can change the key of a composition with a single keystroke.

A number of software programs are available for composing and editing music that conforms to the MIDI standard. They offer a variety of functions: for instance, when you play a tune on a keyboard connected to a computer, a music program can translate what you play into a written score.

WAV sound files end with a .wav extension and can be played by nearly all Windows applications that support sound. This format for storing sound in files developed jointly by Microsoft and IBM was built into Windows 95

MPEG-1 Audio Layer-3 (MP3) files contain compressed sound that maintains high quality. Many different companies make MP3 players. Numerous Web sites offer thousands of MP3 files that users may download and listen to. Concerns about copyright infringement and piracy have put these sites into national headlines.

Regular audio CDs contain sounds stored in a digital format. A standard audio CD-ROM can store about 74 minutes of sound or 783,216,000 bytes of digital music data. Files this size are too big for Web applications to handle. MP3 compresses the CD audio files so they are only 1/10 of the original size with no detectable loss in quality for most people. A three minute song drops in size from 30MB to 3MB, and the download time is usually measured in minutes instead of hours.

Streaming Media - Most audio and video files are downloaded and saved on a hard disk. Once the entire file is saved, the user can listen to the music or watch the video whenever and as often as they want. If the user has a slow Internet connection, this is the only practical option available because it takes far longer to download the information than it does to play it.

Faster computers and faster Internet connections, coupled with the compressed audio in MP3 file, permit Webcasting or streaming media. Streamed audio files are not stored on the hard drive but are played as they arrive at the computer. Without effective compression and high-speed connections, streamed audio and video are very low quality

RealAudio was developed by RealNetworks and supports FM-stereo-quality sound. RealPlayer provides control over digital media, including thousands of radio stations, video, and MP3 audio. To hear a Web page that includes a RealAudio sound file, you need a RealAudio player or plug-in, a program that is freely available from a number of places. It's included in current versions of both Netscape Navigator and Microsoft Internet Explorer.

Windows Media Player is Microsoft's all-in-one player. Its one interface can play back many digital media formats including video and audio streams, CDs, and downloaded media.