I use AudioParameters.suggestOutputChannels() by PdAudio.initAudio(). The suggested output channel is 2 and the result is the phone speaker goes on.
How to turn on the phone earpiece speaker by libpd in Android?
The AudioManager.STREAM_VOICE_CALL returns 0, but then I do PdAudio.initAudio() with 0 as output channel there is no sound at all.