Play sound on speaker without stopping music on bluetooth

Hi there,


I am quite surprised that I was not able to find a discussion about this already. What I am trying to achieve seems simple, yet impossible.

In a navigation app, somehow my client requested to implement the following behavior : have iOS keep on playing its music over Bluetooth while having turn-by-turn voice instructions from their app through the phone speaker.


So far, what I found is that you can only force sounds to go through phone speaker when using option defaultToSpeaker (only available in category Play And Record) along with PortOverrideSpeaker as overrideOutputAudioPort... however doing so will either pause the music playing over bluetooth or "move" the music to play on speaker as well if "mixWithOthers" or "duckOthers" was also set as an option.


Question will be simple: is this possible? then.. How ?