GENERAL

This document describes how a local program that plays to its speakers can play to a local icecast server and thereby to audio streamers in your network. I discussed this with chatgpt in a session called: Using audio output across programs across your network. https://chatgpt.com/c/697630ec-c84c-832a-8163-8b94be8151c8

• Your Linux apps playing audio → PulseAudio sink For example: audacious
• Encoding (OGG/MP3) → streams to Icecast For example: darkice or ffmpeg
• Icecast source client records the sink’s monitor Icecast sends it over your network

Icecast

You must first install, configure and start icecast:

sudo apt-get install icecast

make a icecast configuration or edit an existing one for a mountpoint:

<mount>
  <mount-name>/system.mp3</mount-name>
  <username>source</username>
  <password>hackme</password>
  <public>1</public>
  <max-listeners>100</max-listeners>
</mount>

enable icecast:

sudo systemctl daemon-reload
sudo systemctl enable icecast2
sudo systemctl start icecast2

Encoding

ffmpeg -f pulse -i default \
	-acodec libmp3lame -b:a 128k \
	-f mp3 icecast://source:hackme@localhost:8000/system.mp3

Coupling

On the command line:

ID=$(pactl list source-outputs | \
  awk '
    /Source Output #/ {id=$3}
    /application.process.binary = "ffmpeg"/ {print id; exit}
  ')
[ -n "$ID" ] && pactl move-source-output "$ID" "$MONITOR"

This does what pavucontrol does with a graphical interface.

The script stream-to-icecast.sh

#!/bin/sh
#See output of: pactl list short sources
SINK="alsa_output.pci-0000_00_1b.0.analog-stereo"
MONITOR="${SINK}.monitor"

#Start ffmpeg
/usr/bin/ffmpeg -f pulse -i default \
  -acodec libmp3lame -b:a 128k \
  -f mp3 icecast://source:hackme@localhost:8000/system.mp3 &
FFPID=$!

#Give PulseAudio time to register the source-output
sleep 2

#Find ffmpeg source-output ID and move it
ID=$(pactl list source-outputs | \
  awk '
    /Source Output #/ {id=$3}
    /application.process.binary = "ffmpeg"/ {print id; exit}
  ')
[ -n "$ID" ] && pactl move-source-output "$ID" "$MONITOR"
wait "$FFPID"

Systemd

If you want to make this automatically start with systemd:

make a unit file ~/.config/systemd/user/stream-to-icecast.service:

Description=Stream system audio to Icecast (MP3)
After=pulseaudio.service
Wants=pulseaudio.service

[Service]
ExecStart=/home/rocus/.local/bin/stream-to-icecast.sh
Restart=always
RestartSec=5

[Install]
WantedBy=default.target

then do:

systemctl --user daemon-reload
systemctl --user enable stream-to-icecast.service
systemctl --user start  stream-to-icecast.service
systemctl --user status stream-to-icecast.service

I use Debian 12. Things like places of files maybe different on your system. ie. systemd user files.