P2: Important Description
The volume control seems on differently or have no effect. Two images were tested on NUC. Both behave differently
The boot2Qt image (see attachments with "boot2Qt_" in the front) can change the volume of playing music only if the music app is running. Due to architectural change, music is now played out-of-process by the Media Simulation Server which means that music keeps playing the background even if the Music apps has been stopped (see AUTOSUITE-666). This is the case as of above and it is OK. The problem seems to be that the volume control UI is not connected to this new server and tries to control the music app.
The Pelux based image built on the internal CI (see the attachments with "pelux_" in the front) behaves differently. Volume controls have an effect only if the Music app is in full screen or there is a widget on the home screen and the music app is in the background. The volume control does not work if the Music app is the background and there is no widget on the home screen.
I retested it on the build #946 from the internal CI:
Neptune 3: 5.13.0 "v5.13.0-1_QtAS-22-gcce694b, 2019-07-19 15:36:59 +0000"
Qt Application Manager: 5.13.0
Qt IVI: 5.13.0
The behaviour on that one is even different than I described before, but now it seems to be more clear what the root cause might be. With the architectural change from above, System UI should use media APIs to change the volume and mute if the Music app is not running
