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README.md

Supported Targets ESP32-H4 ESP32-S31

BAP Broadcast Sink Example

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

Overview

This example acts as a BAP Broadcast Sink. It scans for extended advertisements that carry the Broadcast Audio Announcement Service UUID and whose complete-name AD matches the hard-coded "BAP Broadcast Source" string; on a hit, it creates a periodic-advertising sync, builds a BAP broadcast sink for that PA handle and broadcast ID, decodes the BASE / BIGInfo from the PA channel, and then synchronizes to the BIG to receive BIS streams.

The build runs on top of the selected BLE host stack (Bluedroid by default; NimBLE via the sdkconfig.defaults.nimble overlay) and the ESP BLE Audio component set. Sink-side APIs used: esp_ble_audio_common_init / _start, esp_ble_audio_pacs_register + esp_ble_audio_pacs_cap_register (sink PAC and sink location enabled), esp_ble_audio_bap_scan_delegator_register (so a Broadcast Assistant can drive PA-sync, broadcast-code, and BIS-sync requests via BASS), esp_ble_audio_bap_broadcast_sink_register_cb, esp_ble_audio_bap_broadcast_sink_create / _sync / _stop / _delete, and esp_ble_audio_bap_base_get_subgroup_count / _get_bis_indexes. PAC capabilities are LC3 with sample rates 16 kHz + 24 kHz, frame duration 10 ms, 1 channel, 40–60 octets/frame, 1 frame/SDU. The fallback broadcast code is "1234"; if a Broadcast Assistant has supplied one through BASS it is used instead.

After PA sync is established, scan_stop() halts the extended scanner — BASE/BIGInfo arrive over the PA channel — and pa_sync_lost() calls scan_start() to re-arm. The host-specific GAP/PA-sync plumbing lives in main/bluedroid/scan.c and main/nimble/scan.c; main.c only sees the host-agnostic interface in scan.h.

Requirements

  • A board with Bluetooth LE 5.2, ISO, and LE Audio support (e.g. ESP32-H4, ESP32-S31)
  • A peer running the broadcast_source example (or another BAP Broadcast Source advertising the matching name)

Configuration

Open menuconfig:

idf.py menuconfig

No build-time options — runtime defaults are baked into source. The example always runs both: it scans for "BAP Broadcast Source" directly and registers a BASS scan delegator so a Broadcast Assistant could also drive sync (PAST is rejected — see pa_sync_req_cb).

Security & Pairing

The example inherits a Just-Works pairing model (LE Secure Connections, no MITM, no I/O capability) with bonding enabled from the shared init at ../common_components/example_init/ble_audio_example_init.c; change pairing/IO-cap there if needed.

Build & Flash

The base sdkconfig.defaults defaults to the Bluedroid host; idf.py automatically merges the per-target overlay (sdkconfig.defaults.$IDF_TARGET). To build with NimBLE host instead, layer sdkconfig.defaults.nimble on top via -DSDKCONFIG_DEFAULTS.

Bluedroid host (default)

idf.py set-target esp32h4
idf.py -p PORT flash monitor

NimBLE host

idf.py set-target esp32h4
idf.py -DSDKCONFIG_DEFAULTS="sdkconfig.defaults;sdkconfig.defaults.esp32h4;sdkconfig.defaults.nimble" -p PORT flash monitor

For esp32s31, replace the chip overlay accordingly.

(Exit serial monitor with Ctrl-].)

Example Flow

  1. app_main initializes NVS, calls bluetooth_init(), and calls esp_ble_audio_common_init(&info) with info.gap_cb = iso_gap_app_cb.
  2. PACS is registered (snk_pac + snk_loc), each stream's ops field is wired to stream_ops, and the LC3 sink capability is registered via esp_ble_audio_pacs_cap_register(ESP_BLE_AUDIO_DIR_SINK, ...).
  3. The scan delegator (scan_delegator_cbs: recv_state_updated, pa_sync_req, pa_sync_term_req, broadcast_code, bis_sync_req) and broadcast-sink callbacks (base_recv, syncable) are registered, then esp_ble_audio_common_start(NULL) runs.
  4. scan_init() performs host-specific GAP setup (Bluedroid: registers the GAP callback for *_COMPLETE_EVT semaphore signalling + posts EXT_ADV_REPORT / PERIODIC_ADV_SYNC_ESTAB / PERIODIC_ADV_REPORT / PERIODIC_ADV_SYNC_LOST to the audio engine; NimBLE: no-op — the scan-instance callback is passed at ble_gap_disc / ble_gap_periodic_adv_sync_create time). scan_start() then runs passive extended discovery (itvl=window=160). For each ESP_BLE_AUDIO_GAP_EVENT_EXT_SCAN_RECV, data_cb matches the complete/short/broadcast name AD type against "BAP Broadcast Source" and records the Broadcast ID from the Broadcast Audio Service Data.
  5. On match (and only when not already PA-syncing and no scan-delegator state is pinned), pa_sync_create(addr_type, addr, sid) invokes the host-specific PA-sync create routine (ble_gap_periodic_adv_sync_create / esp_ble_gap_periodic_adv_create_sync) with skip=0, sync_timeout=10s.
  6. ESP_BLE_AUDIO_GAP_EVENT_PA_SYNC clears pa_syncing, cancels discovery, stores sync_handle, and calls esp_ble_audio_bap_broadcast_sink_create().
  7. base_recv_cb extracts the subgroup count and BIS index bitfield (masked by bis_index_mask); when no Broadcast Assistant is connected, requested_bis_sync defaults to ESP_BLE_AUDIO_BAP_BIS_SYNC_NO_PREF.
  8. syncable_cb AND-masks the BASE bitfield with the requested mask, copies TARGET_BROADCAST_CODE if the BIG is encrypted (unless BASS already supplied one), and calls esp_ble_audio_bap_broadcast_sink_sync() with the chosen mask and streams_p.
  9. stream_started_cb resets per-stream RX metrics and increments stream_count_started; stream_recv_cb updates metrics via example_audio_rx_metrics_on_recv(). When all streams have stopped, stream_stopped_cb deletes the broadcast sink. pa_sync_lost() clears the cached req_recv_state, deletes any sink, and restarts the scanner.

Expected Log

I (xxx) BAP_BSNK: Scanning for broadcast source...
I (xxx) BAP_BSNK: Broadcast source PA synced, creating Broadcast Sink
I (xxx) BAP_BSNK: BASE received (... subgroup(s))
I (xxx) BAP_BSNK: bis_index_bitfield = 0x...
I (xxx) BAP_BSNK: Broadcast sink syncable, BIG encrypted
I (xxx) BAP_BSNK: Syncing to broadcast: BIS mask 0x... (... stream(s))
I (xxx) BAP_BSNK: [SNK #0] Stream started (.../...)

Per-stream RX metrics are then emitted under the BAP_BSNK tag, name SNK #<idx>. If a Broadcast Assistant connects via BASS, additional log lines appear:

I (xxx) BAP_BSNK: Receive state updated, pa_sync 0x... encrypt 0x...
I (xxx) BAP_BSNK: Received request to sync to PA (PAST {not }available): ...
I (xxx) BAP_BSNK: Broadcast code received
I (xxx) BAP_BSNK: BIS sync req: broadcast_id 0x... BIS mask 0x... subgroup mask 0x... (...)
I (xxx) BAP_BSNK: Received request to terminate PA sync

On teardown / sync loss:

I (xxx) BAP_BSNK: [SNK #0] Stream stopped, reason 0x... (.../...)
I (xxx) BAP_BSNK: PA sync lost: sync_handle ... reason 0x...
I (xxx) BAP_BSNK: PA sync terminated

Peer Pairing

Run broadcast_source on a second board. Expected interaction sequence:

  1. Source advertises extended PDU containing the Broadcast Audio Announcement Service UUID, Broadcast ID 0x123456, and complete name "BAP Broadcast Source"; sink scans and matches by name + UUID.
  2. Source's periodic advertising carries the encoded BASE; sink establishes PA sync and parses the BASE to recover subgroup count and BIS index bitfield.
  3. Source's BIGInfo advertises the BIG as encrypted (broadcast code "1234"); sink reports BIG encrypted.
  4. Source starts the BIG and the two BIS streams (FRONT_LEFT, FRONT_RIGHT); sink calls esp_ble_audio_bap_broadcast_sink_sync() with the chosen BIS bitfield and the matching broadcast code.
  5. Source's TX scheduler keeps pushing SDUs at preset_active.qos.interval; sink stream recv callbacks deliver the data and update RX metrics.
  6. Stopping the source (or losing PA sync) triggers stream_stopped_cb on the sink, which deletes the broadcast sink and resumes scanning.
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