Skip to content

Bluetooth A2DP

AD2DP Introduction

A2DP stands for Advanced Audio Distribution Profile. This is the Bluetooth Stereo profile which defines how high quality stereo audio can be streamed from one device to another over a Bluetooth connection - for example, music streamed from a mobile phone to wireless headphones.

Although many products may have Bluetooth enabled for voice calls, in order for music to be streamed from one Bluetooth device to another, both devices will need to have this A2DP profile. If both devices to do not contain this profile, you may still be able to connect using a standard Headset or Handsfree profile, however these profiles will not support stereo music.

BlueZ5 configuration currently supports A2DP both in server and client mode.

Please note that to correctly work, both HCI interface and bluez-alsa server must be up & running. Please refer to FAQ section for further details

Server Mode

In server mode, you can connect the board via BT to a PC or a mobile phone and play an A2DP audio stream using on-board headphones connector.

Playback from external BT source

  1. Connect headphones or speakers to the on-board headphones connector
  2. Put the external device into pairing mode.
  3. Make sure the external device is discoverable.
# bluetoothctl
[bluetooth]# discoverable-timeout 180
[bluetooth]# discoverable on
  1. Scan and connect the external device to Variscite board.
# bluetoothctl
[bluetooth]# power on
[bluetooth]# agent on
[bluetooth]# default-agent
[bluetooth]# pairable on
[bluetooth]# scan on

Copy mac address

[bluetooth]# scan off
[bluetooth]# pair <mac address>

Approve pairing on the device if required

[bluetooth]# trust <mac address>
[bluetooth]# connect <mac address>
[bluetooth]# quit

  1. On the client side, connect to the device Variscite and play sound through it.

  2. Run bluealsa-aplay on device to play audio through on-board headphones or speakers:

# bluealsa-aplay <mac address>

Recording from external BT source

  1. Follow the steps above to pair and connect with external BT device
  2. Check cards availability
# bluealsa-aplay -L

If no cards appear, confirm you're paired with a device

  1. recording audio originated by external BT source using the results from step 2:
# arecord -f cd -D bluealsa:SRV=org.bluealsa,DEV=XX:XX:XX:XX:XX:XX,PROFILE=a2dp test.wav

Client Mode

In client mode, you can connect and play A2DP audio stream using bluetooth headphones.

Prepare the server device

Make sure the server device is discoverable.

# bluetoothctl
[bluetooth]# discoverable-timeout 180
[bluetooth]# discoverable on

Connect

Into the console of the client device:

  1. Start utility "bluetoothctl":
# bluetoothctl

example:

# bluetoothctl
[NEW] Controller F8:DC:7A:07:8D:A6 VAR-A2DP [default]
[NEW] Device C8:14:79:27:F1:82 SM-T315
[bluetooth]#
  1. Prepare to сonnection:
[bluetooth]# power on
[bluetooth]# agent on
[bluetooth]# default-agent

example:

[bluetooth]# power on
Changing power on succeeded
[bluetooth]# agent on
Agent registered
[bluetooth]# default-agent
Default agent request successful
[bluetooth]#

  1. The first time only, to connect BT headphones, make sure they are in pairing mode. They need to show up in the scan.

  2. Enable scanning

[bluetooth]# scan on

example:

[NEW] Device 68:DF:DD:5D:CF:96 malupas
[NEW] Device 00:06:F7:B3:E9:ED MM100
[NEW] Device 00:07:80:41:68:15 KTS540_0000000
[NEW] Device C8:14:79:27:F1:82 SM-T315
[bluetooth]# scan on
Discovery started
[CHG] Controller F8:DC:7A:07:8D:A6 Discovering: yes
[CHG] Device 00:06:F7:B3:E9:ED RSSI: -57
[CHG] Device 00:07:80:41:68:15 RSSI: -65
[CHG] Device 68:DF:DD:5D:CF:96 RSSI: -98
[CHG] Device 00:07:80:41:68:15 RSSI: -73

"[NEW] Device 00:06:F7:B3:E9:ED MM100" are BT headphones.

  1. Disable scanning
[bluetooth]# scan off

example:

[bluetooth]# scan off
Discovery stopped
[CHG] Controller F8:DC:7A:07:8D:A6 Discovering: no
[bluetooth]#
  1. Pair the device
[bluetooth]# pair 00:06:F7:B3:E9:ED
  1. Connect the device
[bluetooth]# connect 00:06:F7:B3:E9:ED

example:

[bluetooth]# connect 00:06:F7:B3:E9:ED
Attempting to connect to 00:06:F7:B3:E9:ED
[CHG] Device 00:06:F7:B3:E9:ED Connected: yes
Connection successful
[MM100]#
  1. Trust the device
[MM100]# trust 00:06:F7:B3:E9:ED

example:

[MM100]# trust 00:06:F7:B3:E9:ED
[CHG] Device 00:06:F7:B3:E9:ED Trusted: yes
Changing 00:06:F7:B3:E9:ED trust succeeded
[MM100]#
  1. quit from bluetoothctl console
[MM100]# quit

example:

[MM100]# quit
[DEL] Controller F8:DC:7A:07:8D:A6 VAR-A2DP [default]
#

play test sound using MM100 headphones

  1. Follow the steps above to pair and connect with external BT device
  2. Check cards availability
# bluealsa-aplay -L
  1. Play audio to bluetooth speaker using device from the previous step
# aplay -D bluealsa:SRV=org.bluealsa,DEV=FC:A8:9A:EB:8F:B5,PROFILE=a2dp  /usr/share/sounds/alsa/Front_Center.wav

FAQ

  1. The sound doesn't play using headphones connector (board in server mode) or BT headphones (board in client mode).

ALSA may be configured incorrectly, use this command:

# amixer set 'Output Mixer HiFi' on

HCI interface may be down, use this command:

# hciconfig hci0 up