What exactly does Audio Normalisation?

[RostigerSpieler]

I keep a very close eye on what various functions in Jellyfin do. However, it is completely unclear to me what exactly ‘Audio Normalisation’ does?

Yes, I know what this function should do. However, I have almost 2000 films in my library and when I start the Audio Normalisation Process, it is finished within seconds. And that's with so many films and series.

Is it possible that this function is not working?
Because no scan of such a large database can be that fast. And I don't hear any change in the volume of my films after a scan.

And if the function does work. Are the changes saved in the video files?