Advanced Audio Distribution Profile (A2DP)
This profile defines how multimedia audio can be streamed from one device to another over a Bluetooth connection (it is also called Bluetooth Audio Streaming). For example, music can be streamed from a mobile phone, to a wireless headset, hearing aid/cochlear implant streamer, car audio, or from a laptop/desktop to a wireless headset; also, voice can be streamed from a microphone device to a recorder on a PC. The Audio/Video Remote Control Profile (AVRCP) is often used in conjunction with A2DP for remote control on devices such as headphones, car audio systems, or stand-alone speaker units. These systems often also implement Headset (HSP) or Hands-Free (HFP) profiles for telephone calls, which may be used separately.
Each A2DP service, of possibly many, is designed to uni-directionally transfer an audio stream in up to 2 channel stereo, either to or from the Bluetooth host. This profile relies on AVDTP and GAVDP. It includes mandatory support for the low-complexity SBC codec (not to be confused with Bluetooth's voice-signal codecs such as CVSDM), and supports optionally MPEG-1 Part 3/MPEG-2 Part 3 (MP2 and MP3), MPEG-2 Part 7/MPEG-4 Part 3 (AAC and HE-AAC), and ATRAC, and is extensible to support manufacturer-defined codecs, such as aptX.
Some Bluetooth stacks enforce the SCMS-T digital rights management (DRM) scheme. In these cases, it is impossible to connect certain A2DP headphones for high quality audio.