TODO
WiFi
boot only after network is available
SSH
audio jack as default output

sudo apt install gstreamer1.0-tools gstreamer1.0-alsa gstreamer1.0-plugins-good

gst-launch-1.0 -v tcpclientsrc host=192.168.1.197 port=5555 ! 'audio/x-alaw, rate=(int)44100, channels=(int)1' ! alawdec ! alsasink

# /etc/systemd/system/gst-audio-sink.service

[Unit]
Description=GST Audio Sink
After=network.target

[Service]
User=pi
WorkingDirectory=/home/pi
ExecStart=/usr/bin/gst-launch-1.0 -v udpsrc address=224.222.222.222 port=5555 caps='application/x-rtp' ! rtppcmadepay ! alawdec ! alsasink
Restart=always
RestartSec=5

[Install]
WantedBy=multi-user.target

Use IP multicast.

gst-launch-1.0 -v udpsrc address=224.222.222.222 port=5555 caps='application/x-rtp' ! rtppcmadepay ! alawdec ! alsasink