Question about esp_bt_audio for AuraCast broadcast (AUD-7269)

[huming2207]

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Issue or Suggestion Description

Hi @jason-mao @JosephTang

I've got an ESP32-S31 dev board from Taobao and I'm trying to implement an Auracast public broadcast source demo, so that: 1. in the short term, I bring the demo to an audiologist and ask her to test with their hearing aid; and 2. after getting it to work, I may hand over the project to my company. We then make it as a product that can be integrated to a passenger information display system in a tram or bus station and broadcast the audio announcement over BLE, so that hearing impaired people can hear the announcement over their hearing aid.

Currently I'm working on my own with some helps from LLMs. Here are some questions I would like to ask:

1. Maybe I missed out something, but I guess the esp_bt_audio at the moment doesn't support Auracast broadcasting but only support receiving a broadcast. It only initialise the BLE peripherals for me, and I call NimBLE & LC3 codec APIs to send off my audio stream. Is that correct? Do I need to do anything else? Or in other word, should I follow this demo: https://github.com/espressif/esp-idf/blob/master/examples/bluetooth/esp_ble_audio/bap/broadcast_source and add the PBP to publicly announce my broadcast source?
2. If I somehow implement the broadcast right now, then I guess I might need to do this below:

• Add BLE PBP for public broadcasting, otherwise hearing aids/earbuds can't discover the broadcast source?
• For our use cases, stability is more important than audio quality. Then I guess I need to change the hard coded ESP_BLE_AUDIO_BAP_LC3_BROADCAST_PRESET_48_2_1_DEFINE() at

  esp-gmf/packages/esp_bt_audio/src/le/profiles/bap/bt_audio_le_broadcast_source.c

  Line 43 in efc94f5

  ESP_BLE_AUDIO_BAP_LC3_BROADCAST_PRESET_48_2_1_DEFINE(s_preset, ESP_BLE_AUDIO_LOCATION_MONO_AUDIO,

  to something something else, say 16_2_1 instead?

Regards,
Jackson Hu

[JosephTang]

Hi @huming2207

1. esp_bt_audio supports Auracast broadcasting. However, this functionality is not yet demonstrated in the current examples. A demo showcasing this feature will be included in the upcoming release.
2. esp_bt_audio is responsible for Bluetooth profile initialization, while esp-gmf handles audio encoding and decoding. The esp_bt_audio/examples/bt_audio example demonstrates how to decode audio data and play it back.
3. esp-idf/examples/bluetooth/esp_ble_audio/bap/broadcast_source also demonstrates Broadcast Source initialization, but it does not include the pipeline for decoding the source audio and re-encoding it into LC3.
4. The ESP32-S31 is capable of processing 48 kHz mono audio without modification. Whether any changes are needed ultimately depends on the user's requirements.

[huming2207]

Thanks for your reply @JosephTang

esp-idf/examples/bluetooth/esp_ble_audio/bap/broadcast_source also demonstrates Broadcast Source initialization, but it does not include the pipeline for decoding the source audio and re-encoding it into LC3.

For this one on a few different LLMs (ChatGPT/Codex, DeepSeek etc.) and some online docs I've checked, it seems like I need PBP in addition to what you've done in the broadcast_source for public broadcast in our scenario, is that correct?

[JosephTang]

Hi @huming2207

Yes, PBP defines several roles for broadcast audio applications. However, at this stage, you can still use the BMS role defined in TMAP to meet your requirements. Support for this in the example is already under testing~

[huming2207]

Yes, PBP defines several roles for broadcast audio applications. However, at this stage, you can still use the BMS role defined in TMAP to meet your requirements. Support for this in the example is already under testing~

Understood, thanks. I will have a look.