題：什麼是 A2DP

答：A2DP is short for Advanced Audio Distribution Profile.

http://en.wikipedia.org/wiki/Bluetooth_profile#Advanced_Audio_Distribution_Profile_.28A2DP.29

Bluetooth profile : wireless interface spec for bluetooth-base
communication.
Device 必須相容於 Bluetooth profiles 的子集合以使用 bluetooth 的某些 service.

Profiles 提供 manufactures 必須 follow 的標準，使 devices 能照其行為使用 Bluetooth.

A2DP 定義 "high quality audio 如何從一個device 透過藍芽傳輸 stream 到另一個device.
最典型的例子就是把音樂從 藍芽手機(mobile phone)傳輸到 無線耳機(wireless handset)

流程： bluetooth transceiver encodes incoming audio to
Bluetooth-friendly format,
透過空氣傳輸到 耳機, 然後 decode, play audio.

(高檔的耳機會附加麥克風，並支援 Handset(HSP), Hands-Free(HFP), Audio/Video Remote
Control (AVRCP) prfiles.

A2DP 依賴 AVDTP, GAVDP.
Mandatory support: low complexity SBC codec
Optional support: MPEG-1, MPEG-2, MPEG-4, AAC, ATRAC, 或其他
manufacturer-defined codec.