If you are using HDMI or DisplayPort for audio, the devices regularly seem to switch back to in-built audio all by themselves.

This can be due to the HDMI device becoming unavailable when the monitor turns itself off, causing PulseAudio to choose a different device. This causes a problem as PulseAudio does not automatically go back to the originally selected device once the HDMI device has returned.

This is very frustrating as it means constantly having to re-selected the prefered device.

To resolve this problem it is possible to disable automative port switching.

To do this follow the instructions below:

Edit the following file:

vi /etc/pulse/default.pa

Find and comment out the following line:

load-module module-switch-on-port-available

Now restart PulseAudio

pulseaudio -k

 

This fix was applied on Pop_OS! however, should work with a variety of distros.

Source

https://askubuntu.com/questions/158241/automatically-change-sound-input-output-device

https://askubuntu.com/questions/228619/disable-sound-through-hdmi-permanently