MP3 Surround is a new type of MP3 that supports 5.1 channels of audio. MP3 Surround files have the extension *.mp3 like normal stereo MP3 files and can't easily be distinguished from them. That is possible as MP3 Surround encoded MP3-files are completely backwards compatible with standard MP3. MP3 Surround has been developed by the fathers of MP3, the FhG (IIS) in 2004.
MP3 Surround playback
Due to the backwards compatibility to MP3, any hardware and software MP3 player should be able to play MP3 Surround encoded files - although in stereo only. For the playback of the 5.1 content of MP3 Surround files there aren't that many options at the moment: there is a Winamp plugin and a standalone player, both provided at all4mp3.com. The newest DivX player in the version 6.3.x and above can decode DivX-encoded movies with an MP3 Surround encoded audio part. No hardware player for MP3 Surround exists at the moment.
WORK IN PROGRESS
The data overhead is 16 kbit/s, which allows for file sizes similar to standard stereo MP3 files. The file size is approximately 10% larger that a typical MP3. The current evaluation encoder is licensed for personal and non-commercial uses. An MP3 Surround file can be created from 5 or 6 channels of WAV audio.
In January 2006, Thomson and Fraunhofer IIS also released two new companion technologies: Ensonido, which allows playback of MP3 Surround 5.1 channel sound through stereo headphones, and MP3 SX, which upgrades standard stereo mp3 file to mp3 surround files.