Digital audio players (DAP) were often marketed as MP3 players even if they also supported other file formats and media types.[3][4] The PMP term was introduced later for devices that had additional capabilities such as video playback. Generally speaking, they are portable, employing internal or replaceable batteries, equipped with a 3.5 mm headphone jack which can be used for headphones or to connect to a boombox, shelf stereo system, or connect to car audio and home stereos wired or via a wireless connection such as Bluetooth. Some players also include radio tuners, voice recording and other features.