esp-idf/examples/bluetooth/esp_ble_audio/cap/acceptor

Supported Targets	ESP32-H4

CAP Acceptor Example

(See the README.md file in the upper level examples directory for more information about examples.)

This example demonstrates the Common Audio Profile (CAP) Acceptor functionality. It advertises so that a CAP Initiator can connect and set up available audio streams. The acceptor operates in one of two mutually exclusive modes selected at build time: as a BAP Unicast Server (unicast mode, for use with a CAP Initiator) or as a BAP Broadcast Sink (broadcast mode). In broadcast mode, it can be configured to scan for broadcast sources by itself, or to wait for a Broadcast Assistant to connect and direct the sync. Run it together with the initiator example on another device as the CAP Initiator.

The implementation uses the NimBLE host stack with ISO and LE Audio support, ESP-BLE-AUDIO (PACS, CAP acceptor, BAP unicast server, BAP broadcast sink, BAP scan delegator). Advertising includes the CAS (Common Audio Service) UUID and service data; when unicast is enabled it also advertises ASCS with targeted announcement and sink/source contexts; when broadcast is enabled it can include BASS (Broadcast Assistant) service data. PACS advertises LC3 sink and source capabilities (e.g. 7.5 ms / 10 ms frame, stereo, multiple contexts). The example supports optional Kconfig: unicast, broadcast, self-scan for broadcast sources, device name, and (when self-scan) target broadcast device name and broadcast code.

Requirements

• A board with Bluetooth LE 5.2, ISO, and LE Audio support (e.g. ESP32-H4)
• Optionally, another device running the initiator example as CAP Initiator (for unicast and/or as Broadcast Assistant)

How to Use Example

Before project configuration and build, set the correct chip target:

idf.py set-target esp32h4

Configure the Project

Open the configuration menu to select the mode:

idf.py menuconfig

Under Example: CAP Acceptor, select one of:

• Unicast — act as a BAP Unicast Server; start connectable advertising for a CAP Initiator
• Broadcast — act as a BAP Broadcast Sink; receive broadcast audio. When this mode is selected, you can additionally enable:
  • Scan for Broadcast Sources without Broadcast Assistant — start scanning for broadcast sources independently, without waiting for a Broadcast Assistant to connect

Build and Flash

Run the following to build, flash and monitor:

idf.py -p PORT flash monitor

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

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

Example Flow

1. Initialization: NVS, Bluetooth stack, and LE Audio common layer (esp_ble_audio_common_init) with GAP and GATT callbacks. Register PACS (sink and source PAC and location), register sink and source capabilities (LC3), set PACS location and supported/available contexts (init_cap_acceptor). In unicast mode, initialize the CAP acceptor unicast part (BAP unicast server, stream alloc/release). In broadcast mode, initialize the CAP acceptor broadcast part (BAP broadcast sink, scan delegator). Start the audio stack and set the device name.
2. Scan (optional): In broadcast mode with self-scan enabled, start scanning for broadcast sources before or in addition to advertising.
3. Advertising: Start connectable extended advertising with flags, CAS service data, and additionally ASCS service data in unicast mode or BASS service data in broadcast mode, plus device name (cap_acceptor).
4. Initiator connection (unicast mode): When a CAP Initiator connects, the peer connection handle is stored. On MTU exchange the acceptor may start GATT service discovery. The initiator discovers ASEs and sets up unicast streams; the acceptor allocates streams and reports stream released when appropriate.
5. Broadcast (broadcast mode): On PA sync events the acceptor syncs to the broadcast stream; on PA sync lost it handles disconnection. With self-scan, scan results are processed to sync to the chosen broadcast source.

Example Output

I (xxx) CAP_ACC: Extended adv instance 0 started
I (xxx) CAP_ACC: connection established, status 0
I (xxx) CAP_ACC: gatt mtu change, conn_handle 1, mtu  ...
...
I (xxx) CAP_ACC: PA synced, handle 0x... status 0x00
...
I (xxx) CAP_ACC: Sink stream released

If the connection is lost:

I (xxx) CAP_ACC: connection disconnected, reason 0x...
I (xxx) CAP_ACC: PA sync lost, handle 0x... reason ...