Executing a script when pipewire opens a stream

Question

I am running Pipewire with Wireplumber on Ubuntu 21.10. I would like to execute a script when any application starts recording (e.g. when I go into a meeting and the application opens the microphone) This is not just for Zoom, it should work with any application including browser-based. My use case is to turn on a light via OpenHAB when I'm in a meeting. At the moment we use Zoom, Gather, Slack and Discord, and who knows what in the future.

My thought was to monitor Pipewire/Wireplumber to see when an application opens a source stream, but I can't find how to hook that up. Any ideas?

Answer 1

Here's what I came up with, taking advantage of the fact that pactl also works with PipeWire:

#!/bin/bash

source_number=""

pactl subscribe | while read x event y type num; do
    if [ $event == "'new'" -a $type == 'source-output' ]; then
        source_number=$num
        notify-send -u normal -a "Microphone Monitor" "Microphone ON" "Microphone has been turned ON"
        echo "$(date -Is) Microphone on"
    fi

    if [ $event == "'remove'" -a $type == 'source-output' -a $num == "$source_number" ]; then
        source_number=""
        notify-send -u normal -a "Microphone Monitor" "Microphone OFF" "Microphone has been turned OFF"
        echo "$(date -Is) Microphone off"
    fi
done