To create a respawn service with systemd just create a file in /etc/systemd/system/ i.e. mplayer2.service
[Unit]
Desription=mplayer with systemd, respawn
After=network.target
[Service]
ExecStart=/usr/bin/mplayer -nolirc -ao alsa -vo null -really-quiet
http://stream.sunshine-live.de[..]cebook-og-audio-tag/[link1]
Restart=always
[Install]
WantedBy=multi-user.target
and activate it
systemctl enable mplayer2.service
reboot or start it manually
systemctl daemon-reload
systemctl start mplayer2.service
If you reboot or kill the process, it will be restarted automatically some seconds later.