OK, you have me... What is this stuff?

MP3

"MPEG Audio Layer 3", (never MPEG3, by the way - that doesn't exist) is a subset of the MPEG standard for A/V storage. It is an audio format that produces highly compressed files while sacrificing very little audio quality - the perceived frequency response and signal-to-noise ratio are retained. Essentially, MP3 works by removing inaudible information. Compression ratios of up to 12:1 (for stereo files) can be achieved with very little degradation. MP1 and MP2 are similar, but use less complex algorithms and do not compress as well. MP2 is used on VideoCD.

MP3Pro

This is a modified version of mp3 that is backward compatible. It uses 'Spectral Band Replication' to give a greater percieved frequency response in low datarate files by reconstructing harmonics. A file encoded with MP3Pro will playback normally on a regular mp3 player, but will give better quality on a MP3Pro player. The primary target is streaming (Internet radio).

TwinVQ (VQF)

"Time-domain weighted vector interleve quantization" was developed by NTT for Yamaha. It is a different approach to audio compression that can provide high-quality at datarates lower than mp3 (about 18:1 compression). The main disadvantages of vqf now is that it is newer (and therfore less supported) and the encoders are also quite slow. The compression is much different from mp3 and 'breaks-down' under different conditions.

MP4

The name MP4 is mainly to accociate it with MP3. It is actually a collection of codecs including Text-to-speech, MIDI playback (and others) as well as 2 music encoding formats called TF (Time-Frequency) codecs. The standard includes TwinVQ compression (above) as one of the TF codecs, the other is AAC (below).

AAC

"Advanced Audio Coding" is an extension of MPEG-2 Audio Layer 3 NBC (non backward compatible). It can encode with greater quality and lower datarate than MP3. It also supports multichannel audio including LFE (low-frequency effects channels used in movies) and sounds better than Dolby AC3 currently used in Dolby Digital movies and DVD's at the same bitrate (assuming a good encoder is used). Normal (low-complexity) AAC files can be found in the iTunes musin store. The technically superior high-efficiency AAC is more rare, but is supported by Nero.

OGG Vorbis

Cool name! This is an open source, community developed, audio encoding format along the same lines as mp3 and mp4. It provides very good quality and is being worked on by many people who care about it's performance. It fully supports multicahnnel with bitrates typically lower than Dolby AC3. Unlike other formats it is free of licensing fees so you can develop commercial hardware and software incorporating it's technology without having to go broke doing so. This link to their site is the only encoding software link on this page. Think about why.

MP3 Playback capability has been integrated into many media applications including Windows media player, RealAudio player and Apple Quicktime. A number of handheld devices exist and you can now carry a few hours worth of compressed music with you anywhere. Car based mp3 players with capabilities like the eMpeg* may soon be available in the mainstream US aftermarket and eventually direct from the Auto manufacturers. So-called MP3cd players from Kenwood and AIWA which can take computer CD-ROM's with MP3 files on them and play them back in your car started shipping in 2000-06 (and no, I don't have one). Modern DVD players boast mp3 playback too.

*The EMPEG player has been scooped up by Diamond Multimedia. Diamond fought the first court battle to allow portable hardware mp3 players to be produced. They were acquired by the graphics chipset developer, S3, and the new company is called SonicBlue... OK, now it's RioAudio (2003.04) and the eMpeg car unit's have been gone for over a year :-( but they make lots of portables, including HD-based ones. Seriously though, just get an iPod.