is this libary single threaded?

[pixmusix]

If I use this library will I have a free core to do more work without disturbing the audio? :)
Does it use two cores behind the scene?

[pschatzmann]

The ESP32 runs the Bluetooth stack on core 0 and the Arduino code on core 1.
The A2DP task is running on the core configured with the set_task_core(BaseType_t core) method; by default it is core 1.

[pixmusix]

Thanks @pschatzmann for taking the time to answer.
That clears up a lot.

I think what I'm learning from the docs is that a function like get_data_frames() is defined in core0 and then passed into and runs in core1.
Is that correct?

If that's the case, then, to update the callback I can give it volatile data?
For example this seems to compile:

#include "BluetoothA2DPSource.h"
#include <math.h> 

#define c3_frequency  130.81
#define D_PHA  0.01
#define DELAY_MS   2

volatile float PHASE = 0.0;

BluetoothA2DPSource a2dp_source;

int32_t get_data_frames(Frame *frame, int32_t frame_count) {
    static float m_time = 0.0;
    float m_amplitude = 10000.0; 
    float m_deltaTime = 1.0 / 44100.0;
    float pi_2 = PI * 2.0;

    float m_phase = PHASE; // <<---- VOLATILE

    for (int sample = 0; sample < frame_count; ++sample) {
        float angle = pi_2 * c3_frequency * m_time + m_phase;
        frame[sample].channel1 = m_amplitude * sin(angle);
        frame[sample].channel2 = frame[sample].channel1;
        m_time += m_deltaTime;
    }

    delay(DELAY_MS);

    return frame_count;
}

void setup() {
  a2dp_source.set_auto_reconnect(false);
  a2dp_source.set_data_callback_in_frames(get_data_frames);
  a2dp_source.set_volume(30);
  a2dp_source.start("MY_BT_HEADPHONES");  
}

void loop() {
  PHASE = fmod(PHASE + D_PHA, 1.0);
  delay(DELAY_MS);
}

[pschatzmann]

I am note sure: I guess this is directly called by the bluetooth stack, so I would be from core 0.
Why don't you just write a simple test sketch by calling xPortGetCoreID() ?

[pixmusix]

@pschatzmann I guess this is directly called by the bluetooth stack, so I would be from core 0.

Sounds like experiments required. Will report back. :)