tl;dr: Is it possible to control the volume of the Amp2/HifiBerryOS with the buttons of my smartphone in sync? (So when the smartphone shows the maximum volume, the Amp2 is playing at the maximum volume level too?)
I have a Raspberry Pi 4 with an Amp2 and the latest HifiBerry OS. No other components, everything is working fine except one thing:
The volume control is not in sync with the volume control on my smartphone. It doesn't matter if I use Airplay or Bluetooth.
After booting Hifiberry OS the default volume level of the Amp2 is different to the current volume level on my smartphone. This difference is there the whole time. So I'm not able to control the volume of the HifiberryOS/Amp2 correctly with my smartphone.
After booting Hifiberry OS I'm starting playing some music - let's say via Airplay. Now I'm lowering the volume with the buttons of my iPhone. I can hear that the volume actually goes down - but not in the same steps as on my iPhone. At the end the iPhone shows that the music should be mute, but I can still hear the music (quietly) through the speakers. And the web interface of the Hifiberry OS is telling me that the volume is still at round about 25 percent.
This behaviour is the same on all smarpthones and tablets I've available. And it doesn't matter if I use the (real) volume buttons or the volume control of a media player app. To control the volume in a correct manner, I have to use the controls of the HifiberryOS web interface.
Is it possible to "sync" the controls? Do I overlooked something?