Linux raspberrypi 5.4.83-v7l+ #1379 SMP Mon Dec 14 13:11:54 GMT 2020 armv7l

The programs included with the Debian GNU/Linux system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.

Debian GNU/Linux comes with ABSOLUTELY NO WARRANTY, to the extent
permitted by applicable law.

pi@raspberrypi:~ $ sudo usermod -G bluetooth -a pi

# logout

pi@raspberrypi:~ $ sudo apt update && sudo apt upgrade -y && sudo apt install bluealsa -y
pi@raspberrypi:~ $ sudo service bluealsa start
pi@raspberrypi:~ $ bluetoothctl 
Agent registered
[bluetooth]# scan on
Discovery started
[CHG] Controller 00:00:00:00:00:00 Discovering: yes
[bluetooth]# pair FF:FF:FF:FF:FF:FF
Attempting to pair with FF:FF:FF:FF:FF:FF
[CHG] Device FF:FF:FF:FF:FF:FF Connected: yes
[CHG] Device FF:FF:FF:FF:FF:FF ServicesResolved: yes
[CHG] Device FF:FF:FF:FF:FF:FF Paired: yes
Pairing successful
[CHG] Device FF:FF:FF:FF:FF:FF ServicesResolved: no
[CHG] Device FF:FF:FF:FF:FF:FF Connected: no
[bluetooth]# trust FF:FF:FF:FF:FF:FF
[CHG] Device FF:FF:FF:FF:FF:FF Trusted: yes
Changing FF:FF:FF:FF:FF:FF trust succeeded     
[bluetooth]# connect FF:FF:FF:FF:FF:FF
Attempting to connect to FF:FF:FF:FF:FF:FF
[CHG] Device FF:FF:FF:FF:FF:FF Connected: yes
Connection successful
[BT DEVICE]# quit
pi@raspberrypi:~ $ echo "defaults.bluealsa {
>     interface "hci0"
>     device "FF:FF:FF:FF:FF:FF"
>     profile "a2dp"
> }" | sudo tee /etc/asound.conf
defaults.bluealsa {
	interface hci0
	device FF:FF:FF:FF:FF:FF
	profile a2dp
}
pi@raspberrypi:~ $ aplay -D bluealsa /usr/share/sounds/alsa/Front_Center.wav
Playing WAVE '/usr/share/sounds/alsa/Front_Center.wav' : Signed 16 bit Little Endian, Rate 48000 Hz, Mono

pi@raspberrypi:~ $ sudo apt install -y python3-pip mpv && sudo apt purge -y youtube-dl && sudo pip3 install youtube-dl
pi@raspberrypi:~ $ mpv --volume=50 --no-video --audio-device=alsa/bluealsa ytdl://dQw4w9WgXcQ
# connects automatically after reboot - no further setup needed

# optional: disable sap
pi@raspberrypi:~ $ sudo mkdir /etc/systemd/system/bluetooth.service.d/
pi@raspberrypi:~ $ sudoedit /etc/systemd/system/bluetooth.service.d/01-disable-sap-plugin.conf
pi@raspberrypi:~ $ sudo systemctl daemon-reload
pi@raspberrypi:~ $ sudo systemctl restart bluetooth.service