What's a proprietary format?
You have MP3 (MPEG) audio which is based on open standards and then you have proprietary formats which are generally attempts by software companies to generate their own audio format. The reason for developing proprietary formats is often very simple. Profit. If you come up with the next whiz-bang format which becomes enormously popular, there is every chance of building a business model and revenue stream around it. Think of Liquid Audio, which is based on Dolby Digital and MPEG AAC. It's a proprietary format because it bases some of its technology on MPEG audio standards. It supports streaming audio as well as watermarking and encryption. Liquid Audio is a popular format amongst recording artists and labels because the copyright protection dissuades many from attempting to duplicate and distribute unauthorized copies of Liquid Audio encoded songs. Two other proprietary formats (although they are strictly known as non-propriety as they are not based on the MPEG standard) are Real Audio and Windows Media Audio. One issue facing developers of proprietary formats is getting support from music playing software. The starting point for solving this problem is to develop a player as well. Hence the Liquid Player, Windows Media Player and RealPlayer. MPEG-based Proprietary Formats: a2b, MP4, Liquid Audio and Apple Quicktime.
Non-MPEG-based Proprietary Formats: Dolby Digital, EPAC, Windows Media Audio, Real Audio, TAC and TwinVQ (VQF). | 
