Overview of Advanced Audio Distribution Profile (A2DP) (Source Role)

10/16/2008

Windows Embedded NavReady supports the Bluetooth Advanced Audio Distribution Profile (A2DP). Bluetooth A2DP defines the protocols and procedures that let one Bluetooth-enabled device stream advanced audio from audio files to another Bluetooth-enabled device that has high-quality mono or stereo audio-output capabilities.

When a Windows Embedded NavReady powered portable navigation device (PND) supports the Source (SRC) role, it can stream advanced audio from audio alerts, turn-by-turn driving directions from a navigation application, or music content to an in-car media player. Then, the user can listen to the audio through in-car stereo speakers.

A2DP Roles

A2DP lets you create a Bluetooth channel through which advanced audio data is streamed from one Bluetooth-enabled device to another Bluetooth-enabled device.

Two roles are defined for Bluetooth-enabled devices that support A2DP:

• Source (SRC) role: a device is the SRC when it is the source of a digital-audio data and sends the stream to the SNK; for example, a portable navigation device (PND).
• Sink (SNK) role: a device is the SNK when it receives the digital-audio stream delivered from the SRC; for example, an in-car media player.

A Windows Embedded NavReady powered device supports the Source role only.

A2DP Architecture Overview

The following illustration shows the A2DP architecture:

The Windows Embedded NavReady powered device is the SRC that stores audio files in memory. The audio files can be part of a navigation application, or they can be obtained from a desktop media player through a connection to a desktop computer.

To start streaming audio data to a SNK device, the Windows Embedded NavReady powered device pairs to a device, and then searches the Service Discovery Profile (SDP) record on that paired device to determine whether the device supports A2DP. If it does support A2DP, the Windows Embedded NavReady powered device assumes the SRC role and uses the Audio Compression Manager (ACM) to send audio data over a Bluetooth connection.

The Windows Embedded NavReady powered device includes a waveform audio driver for features such as volume control and managing audio lines for playing digital-audio files. To route the audio data to a remote-output destination, the SRC device can use A2DP to stream the audio data over a Bluetooth link to a SNK device that supports mono or stereo audio-output capabilities, such as an in-car Bluetooth device. By using A2DP, audio data is compressed in a suitable format to effectively use bandwidth over a Bluetooth link.

The SNK device uses A2DP to receive the audio data and then uses its media player and audio driver to send it to an audio-output device, such as in-car stereo speakers.

A2DP depends on the General Access Profile in the Bluetooth stack, and also uses Audio/Video Distribution Transport Protocol to handle the streaming of audio data.

ActiveSync Desktop Pass-through (DTPT)

ActiveSync Desktop Pass-through (DTPT) is a technology that enables a Windows Embedded NavReady powered device to access files and features on a desktop computer through an ActiveSync connection that uses either USB, Bluetooth, infrared, or serial communications.

With DTPT, the device can establish a connection to a desktop computer and sync with the digital-audio collection stored on the desktop media player, such as Windows Media Player.

Benefits for Users

With support for A2DP and DTPT on a Windows Embedded NavReady powered portable navigation device (PND), users can store their digital-audio files on the PND and stay connected with their music and audio. Users can set up the PND to sync with their desktop media player. Then, they can copy their digital audio and music to the PND and enjoy their digital audio and music anywhere they go.

With a Bluetooth-enabled in-car media player that supports the Sink (SNK) role, it is easy to create a pairing relationship and use the in-car media player to stream audio to the in-car speakers through A2DP.

Users can also control playback of audio files from the SNK by using the Overview of Audio/Video Remote Control Profile (AVRCP) (Target Role).

Interaction Model for A2DP and Hands-Free Profile (HFP)

Windows Embedded NavReady supports connections to more than one Bluetooth-enabled device. However, the Hands-Free Profile (HFP) port and A2DP port on the Windows Embedded NavReady powered device supports being connected to only one device per profile at a time. They can be the same device, such as a Bluetooth system with a Subscriber Identity Module (SIM) card, phone capabilities, and stereo speakers. Or, one paired phone can be connected through HFP, and one paired in-car media device can be connected through A2DP.

If a user initiates an interaction to connect a new Bluetooth-enabled device to a profile port (HFP or A2DP) that is currently connected to another paired device, the previously-connected device will be disconnected, and the new device will be connected.

If an incoming voice call arrives through HFP, the audio stream through A2DP will be suspended until the hands-free voice call is disconnected.

Support for A2DP in an OS Design

To include support for A2DP, you must include the Advanced Audio Distribution Profile (A2DP) Catalog item (SYSGEN_BTH_A2DP) in your OS design.

To use A2DP to play audio on a Windows Embedded NavReady powered device, you must already have support in your run-time image for playing digital-audio files. For more information, see Waveform Audio.

There are no special A2DP code-implementation requirements to enable A2DP connections from a Windows Embedded CE powered device, other than including support for Bluetooth pairing, including the A2DP Catalog item, and optionally including the Audio/Video Remote Control Profile (AVRCP) Catalog item.

See Also

Concepts

Bluetooth Profiles OS Design Development
ActiveSync Desktop Pass-through (DTPT) for Portable Navigation Devices
Overview of Bluetooth Pairing