A digital music player that supports the MP3 audio format, which started a revolution in online music downloads and distribution (see MP3). All portable music players can read files encoded in MP3 and possibly other formats. For example, the leading digital music player by far is the iPod, and it supports Apple's featured format (see AAC).With a music app built in or available for every smartphone, almost everyone has an MP3 player, resulting in a huge decline in stand-alone MP3 player sales. In addition, CD/DVD players, whether shelf units or portable, may support MP3 files. For more details, see digital music player and iPod. See MP3, audioblog, podcast, codec examples and peer-to-peer network.