This tutorial will convert your Raspberry PI into a Bluetooth receiver, which plays audio wirelessly through connected speakers:

Audio source like iPhone -(((  wireless transmission  )))-> Raspberry PI -> USB Audio -> Speakers

It works like a regular car audio system with Bluetooth but can be used anywhere and supports multiple audio sources.

I'm using Raspberry PI 1 Model B, running Raspbian Jessie. Make the system is up–to–date:

sudo apt-get update
sudo apt-get upgrade

Then install required packages:

http://www.instructables.com/id/Enhance-your-Raspberry-Pi-media-center-with-Blueto/?ALLSTEPS

sudo apt-get install alsa-utils bluez bluez-tools pulseaudio-module-bluetooth python-gobject python-gobject-2

Not quite sure it's really needed (?), but it doesn't hurt:

sudo usermod -a -G lp pi

I used external USB audio interface Creative Sound Blaster Play. The on–board audio produces low–quality, noisy output, so I decided to use something better.

As for Bluetooth dongle, I used Digitus Tiny USB-Adapter, which is discovered as Cambridge Silicon Radio, Ltd Bluetooth Dongle.

Note: I used another dongle (different manufacturer) also discovered as Cambridge Silicon Radio... but unable to stream audio. So beware, because different manufacturers use the same hardware in a different way. Or pretend to use the same hardware for some (compatibility?) reasons. This way or another, if you get garbled audio or no audio at all but everything else is alright, then try another dongle – it's cheap.

See RPi USB Bluetooth adapters for buying recommendations. Trial and error is another option, since most devices cost below $10.

Note: Raspberry PI offers limited power to USB devices (and limited number of ports). You'll need some active (powered) USB Hub to keep USB devices stable and working (USB Audio, USB Bluettoth and optional USB WiFi). Google to learn more, it's a very common hardware problem with Raspberry PI.

pi@raspberrypi:~ $ lsusb
...
Bus 001 Device 008: ID 041e:30d3 Creative Technology, Ltd Sound Blaster Play!
...
Bus 001 Device 012: ID 0a12:0001 Cambridge Silicon Radio, Ltd Bluetooth Dongle (HCI mode)
...

Use the following configuration to get most of PulseAudio.

http://www.crazy-audio.com/2014/09/pulseaudio-on-the-raspbery-pi/

pi@raspberrypi:~ $ cat /etc/pulse/daemon.conf
...
resample-method=ffmpeg
enable-remixing = no
enable-lfe-remixing = no
default-sample-format = s32le
default-sample-rate = 192000
alternate-sample-rate = 176000
default-sample-channels = 2
exit-idle-time = -1
...

Reboot PI:

sudo reboot

Note: PA is pretty CPU–consuming. With the following configuration it uses ~30% of my PI's CPU. So if you expect PI to do something else beside A2DP and avoid sound glitches, reasearch different resample-method.

The problem is that on–board audio ouput is prefered over USB audio interface:

pi@raspberrypi:~ $ cat /proc/asound/modules
 0 snd_bcm2835
 1 snd_usb_audio

Some configuration does the trick and from now on RPI uses USB Audio as default:

http://raspberrypi.stackexchange.com/questions/40831/how-do-i-configure-my-sound-for-jasper-on-raspbian-jessie

pi@raspberrypi:~ $ cat /etc/modprobe.d/alsa-base.conf
# This sets the index value of the cards but doesn't reorder.
options snd_usb_audio index=0
options snd_bcm2835 index=1

# Does the reordering.
options snd slots=snd-usb-audio,snd-bcm2835

Reboot the device:

sudo reboot

See snd_usb_audio as a preferred output:

pi@raspberrypi:~ $ cat /proc/asound/modules
 0 snd_usb_audio
 1 snd_bcm2835

pi@raspberrypi:~ $ cat /etc/bluetooth/audio.conf
[General]
Class = 0x20041C
Enable = Source,Sink,Media,Socket

Reboot PI:

sudo reboot

Pair devices (phones, tablets, PCs) with PI:

bluetoothctl

[bluetooth]# list
Controller 00:1A:7D:DA:71:06 raspberrypi [default]

[bluetooth]# agent on
[bluetooth]# default-agent
[bluetooth]# discoverable on
[bluetooth]# scan on

Then, for each device:

pair XX:XX:XX:XX:XX:XX
trust XX:XX:XX:XX:XX:XX

pi@raspberrypi:~ $ pactl list sources short
0   alsa_output.0.analog-stereo.monitor module-alsa-card.c  s16le 2ch 48000Hz   IDLE
1   alsa_input.0.analog-mono    module-alsa-card.c  s16le 1ch 48000Hz   IDLE
4   bluez_source.A8_88_08_11_AB_4B  module-bluez5-device.c  s16le 2ch 44100Hz   RUNNING

pi@raspberrypi:~ $ pactl list sinks short
0   alsa_output.0.analog-stereo module-alsa-card.c  s16le 2ch 48000Hz   RUNNING

The whole trick to make a2dp work is to redirect a right source (like iPhone) to the right sink (ALSA).

In this example it would be bluez_source.A8_88_08_11_AB_4B -> alsa_output.0.analog-stereo, given that the phone is already paired and connected to PI.

Add udev rule which executes a2dp-autoconnect script each time a bluetooth device is connected

pi@raspberrypi:~ $ sudo cat /etc/udev/rules.d/99-input.rules
KERNEL=="input[0-9]*", RUN+="/home/pi/a2dp-autoconnect"

The script is an extended version of http://blog.mrverrall.co.uk/2013/01/raspberry-pi-a2dp-bluetooth-audio.html. It redirects a new bluetooth device to the right sink and sets the right volume level.

I located it in /home/pi/a2dp-autoconnect, then set it executable:

pi@raspberrypi:~ $ chmod +x a2dp-autoconnect

To observe connection log "live":

pi@raspberrypi:~ $ tail -f /var/log/a2dp-autoconnect