ESP32 HFP AG CVSD data format

[LiborT]

Hi ESP32 community,
I'm trying to understand and modify the HFP AG example for an open-source digital radio amateur transceiver.

What is the format of the data I shall return in the

Code: Select all

static uint32_t bt_app_hf_outgoing_cb(uint8_t *p_buf, uint32_t channel_len)

function? I'm using CVSD (disabled wideband mSBC in menuconfig).
the channel_len is 120, what 120 bytes? words? oranges? Signed or unsigned?

CVSD shall be 64kbit/s -> 8kHz * 8 bits mono, but the example is using int16_t? I'm getting some sound from BT headset, but it's far from sinus. Does it even accept raw audio data? Or does it need to be encoded with some vocoder?

I think it shall be in big-endian int16_t {LSB, MSB, LSB, MSB...} however when I'm packing 2xChannel_len bytes the app crashes.

TNX

Update:
Ok by test&crash I've found it's big-endian int16_t sound indeed, channel_len is byte count. For my HW, it's always 120, also 60 samples also 7.5ms voice per call. It would be nice having it properly documented.