mp4 Players
A digital audio player (DAP) is a device that stores, organizes and plays digital music files. It is more commonly referred to as an mp4 player (because of that format's ubiquity), but DAPs often play many additional file formats. Some formats are proprietary, such as mp4, Windows Media Audio (WMA), and Advanced Audio Codec (AAC). Some of these formats also may incorporate restrictive digital rights management (DRM) technology, such as WMA DRM, which are often part of certain paid download sites. Other formats are completely patent-free or otherwise open, such as Ogg Vorbis, FLAC, and Speex (all part of the Ogg open multimedia project).
There are three main types of digital audio players:
mp4 CD Players - Devices that play CDs. Often, they can be used to play both audio CDs and homemade data CDs containing mp4 or other digital audio files.
Flash-based Players - These are solid state devices that hold digital audio files on internal or external media, such as memory cards. These are generally low-storage devices, typically ranging from 128MB-4GB, which can often be extended with additional memory. As they are solid state and do not have moving parts, they are very resilient. Such players are generally integrated into USB keydrives.
Hard Drive-based Players or Digital Jukeboxes - Devices that read digital audio files from a hard drive. These players have higher capacities, ranging from 1.5GB to 100GB, depending on the hard drive technology. At typical encoding rates, this means that thousands of songs — perhaps an entire music collection — can be stored in one mp4 player. The Apple iPod and Creative Zen are examples of popular digital jukeboxes.