and that's the cheap Shuffle. Unprotected AAC is often described as mp4. If eMusic is the only outfit that can make a business model of this, then the others deserve to die...MP3 (8 to 320 Kbps), MP3 VBR, AAC (8 to 320 Kbps), Protected AAC (from iTunes Music Store, M4A, M4B, M4P), Audible (formats 2, 3, and 4) and WAV. Specs
My big regret is that Fraunhofer gave up the fight and MP3 became the de facto standard, rather than the technically superior MP4.