This example uses the Bluedroid external codec path: the application generates PCM, encodes it to MPEG-2/4 AAC (M24) with esp_audio_codec, and sends the encoded stream.

Required components

espressif/esp_audio_codec

How to use this example

Hardware Required

This example runs on any commonly available ESP32 or ESP32-S31 development board.

It is intended to connect to an A2DP sink that supports AAC, such as A2DP sink stream AAC example.

Configure the project

idf.py menuconfig

Enable Classic Bluetooth and A2DP under Component config --> Bluetooth --> Bluedroid Enable

Build and Flash

Build the project and flash it to the board, then run monitor tool to view serial output.

idf.py -p PORT flash monitor

(Replace PORT with the name of the serial port to use.)

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

For the first step, this example performs device discovery to search for a target device (A2DP sink) whose device name is "ESP_SPEAKER_AAC" and whose "Rendering" bit of its Service Class field is set in its Class of Device (COD). If a candidate target is found, the local device will initiate connection with it.

After connection with A2DP sink is established, the example performs the following running loop 1-2-3-4-1:

audio transmission starts and lasts for a while
audio transmission stops
disconnect with target device
reconnect to target device

The example implements an event loop triggered by a periodic "heart beat" timer and events from Bluetooth protocol stack callback functions.

After the local device discovers the target device and initiates connection, there will be logging message like this:

I (4090) BT_AV: Found a target device, address xx:xx:xx:xx:xx:xx, name ESP_SPEAKER_AAC
I (4090) BT_AV: Cancel device discovery ...
I (4100) BT_AV: Device discovery stopped.
I (4100) BT_AV: a2dp connecting to peer: ESP_SPEAKER_AAC

If connection is set up successfully, there will be such message:

I (5100) BT_AV: a2dp connected

Starting of audio transmission has the following notification message:

I (10880) BT_AV: a2dp media ready checking ...
...
I (10880) BT_AV: a2dp media ready, starting ...
...
I (11400) BT_AV: a2dp media start successfully.
I (11410) BT_AV_AAC: AAC enc: 44100 Hz, ch 2, bitrate 160000 (vbr=0)
I (11420) BT_AV_AAC: stream: 23219 us/frame, 44100 Hz, 1024 samples

Stop of audio transmission, and disconnection with remote device generate the following notification message:

I (110880) BT_AV: a2dp media suspending...
I (110920) BT_AV: a2dp media suspend successfully, disconnecting...
I (111040) BT_AV: a2dp disconnected

Audio content

PCM is a 440 Hz sine tone (stereo by default, 16-bit). Each frame is encoded to AAC and paced to match the negotiated sample rate. On the sink side you should hear a steady tone, not random noise.

Troubleshooting

For any technical queries, please open an issue on GitHub. We will get back to you soon.