Some people have misinterpreted support for the MP3 file format in Active Worlds 3.1 as intended to support full-length CD-quality song files, or to support "streaming" MP3 files.
Outerworlds 3.1 does not support streaming MP3, it simply supports the MP3 file format itself for sound files that are downloaded and played by the browser, the same as WAV files. Furthermore, while in theory a full-length CD-quality song could be used in Outerworlds, the download size of such files (typically several megabytes) are still prohibitive and will prevent most users on low-bandwidth connections from hearing them in a timely fashion.
Support for MP3 files is intended primarily as a replacement for WAV files for all sounds in Outerworlds. The MP3 file format is a far more efficient format than WAV for storing audio. By using MP3, for a given download size (say 100K) a much longer audio clip at a much higher quality can be stored using MP3 versus using WAV.
Making MP3 files
World owners who wish to add MP3 files to their worlds can make use of any of the dozens of free MP3 encoders available on the web. The process is usually as simple as loading an existing WAV file into an MP3 encoding program and getting a MP3 file back out, which can then be uploaded to your world's object path (in the sounds folder) and then used anywhere in your world.
If you don't have a MP3 encoder, try going to www.winfiles.com and searching for "MP3 encoders".
Note: unlike WAV and MID files, MP3 files should not be zipped before uploading to an object path. MP3 files are already highly compressed and usually derive little or no additional benefit from being zipped.
Support for the MP3 file format in Outerworlds 3.1 should not be interpreted as an invitation to begin pirating copyrighted music for use in Outerworlds. The same restrictions that apply to the picture command for image files apply to MP3 files as well: you may not link to MP3 files on other people's sites without their permission, and under no circumstances may you use copyrighted MP3 files without the permission of the author. Linking to copyrighted music without the owner's permission, whether on your web site or theirs, is illegal and could subject you to criminal prosecution!