feat: Add default SBC SEP in A2DP init

components/bt/host/bluedroid/api/include/api/esp_a2dp_api.h

@@ -257,6 +257,7 @@ typedef enum {
     ESP_A2D_SEP_REG_FAIL,                      /*!< A2DP stream endpoint register generic fail */
     ESP_A2D_SEP_REG_UNSUPPORTED,               /*!< A2DP stream endpoint register fail, unsupported codec type or param */
     ESP_A2D_SEP_REG_INVALID_STATE,             /*!< A2DP stream endpoint register fail, invalid state */
+    ESP_A2D_SEP_REG_SBC_REQUIRED,              /*!< A2DP stream endpoint register fail, at least one SBC SEP must remain */
 } esp_a2d_sep_reg_state_t;
 
 /**
@@ -511,7 +512,11 @@ esp_err_t esp_a2d_sink_init(void);
  *                  SEP index repeatedly will overwrite the old one.
  *                  It is necessary to set BT_A2DP_USE_EXTERNAL_CODEC to y.
  *
- * @note            The SEID determines the priority of negotiating the configuration with the peer for initiator.
+ * @note            After A2DP sink init, every SEID is pre-registered with the mandatory default SBC SEP.
+ *                  Calling this API overwrites that SEID. A2DP requires at least one SBC SEP; registering a
+ *                  non-SBC codec that would overwrite the last SBC SEP fails with ESP_A2D_SEP_REG_SBC_REQUIRED.
+ *                  Therefore using AAC (or other non-SBC codecs) requires ESP_A2D_MAX_SEPS >= 2.
+ *                  The SEID determines the priority of negotiating the configuration with the peer for initiator.
  *                  The lower the SEID, the higher the priority of the codec capability.
  *
  * @param[in]       seid: local SEP identifier, start from 0, less than ESP_A2D_MAX_SEPS
@@ -667,7 +672,11 @@ esp_err_t esp_a2d_source_set_pref_mcc(esp_a2d_conn_hdl_t conn_hdl, const esp_a2d
  *                  SEP index repeatedly will overwrite the old one.
  *                  It is necessary to set BT_A2DP_USE_EXTERNAL_CODEC to y.
  *
- * @note            The SEID determines the priority of negotiating the configuration with the peer for initiator.
+ * @note            After A2DP source init, every SEID is pre-registered with the mandatory default SBC SEP.
+ *                  Calling this API overwrites that SEID. A2DP requires at least one SBC SEP; registering a
+ *                  non-SBC codec that would overwrite the last SBC SEP fails with ESP_A2D_SEP_REG_SBC_REQUIRED.
+ *                  Therefore using AAC (or other non-SBC codecs) requires ESP_A2D_MAX_SEPS >= 2.
+ *                  The SEID determines the priority of negotiating the configuration with the peer for initiator.
  *                  The lower the SEID, the higher the priority of the codec capability.
  *
  * @param[in]       seid: local SEP identifier, start from 0, less than ESP_A2D_MAX_SEPS

components/bt/host/bluedroid/bta/av/bta_av_main.c

@@ -542,10 +542,8 @@ static void bta_av_api_register(tBTA_AV_DATA *p_data)
     tAVDT_CS        cs;
     char            *p_service_name;
     tBTA_UTL_COD    cod;
-#if (BTA_AV_EXT_CODEC == FALSE)
     tBTA_AV_CODEC   codec_type;
     UINT8           index = 0;
-#endif
     char p_avk_service_name[BTA_SERVICE_NAME_LEN + 1];
     BCM_STRLCPY_S(p_avk_service_name, BTIF_AVK_SERVICE_NAME, BTA_SERVICE_NAME_LEN + 1);
 
@@ -667,10 +665,25 @@ static void bta_av_api_register(tBTA_AV_DATA *p_data)
 
             /* keep the configuration in the stream control block */
             memcpy(&p_scb->cfg, &cs.cfg, sizeof(tAVDT_CFG));
-#if (BTA_AV_EXT_CODEC == FALSE)
+            /*
-            while (index < BTA_AV_MAX_SEPS &&
+             * Create local SEPs:
-                    (p_scb->p_cos->init)(index, &codec_type, cs.cfg.codec_info,
+             * - Internal codec: init() supplies SBC (typically one SEP).
-                                         &cs.cfg.num_protect, cs.cfg.protect_info, p_data->api_reg.tsep) == TRUE) {
+             * - External codec: A2DP mandates SBC, so pre-fill every SEID with
+             *   the default SBC SEP; app register_stream_endpoint() may overwrite.
+             */
+            while (index < BTA_AV_MAX_SEPS) {
+#if (BTA_AV_EXT_CODEC == TRUE)
+                if (bta_av_co_audio_build_sbc_default(p_data->api_reg.tsep, &codec_type,
+                                                      cs.cfg.codec_info) != TRUE) {
+                    APPL_TRACE_ERROR("failed to build default SBC SEP for seid %d", index);
+                    break;
+                }
+#endif
+                if ((p_scb->p_cos->init)(index, &codec_type, cs.cfg.codec_info,
+                                         &cs.cfg.num_protect, cs.cfg.protect_info,
+                                         p_data->api_reg.tsep) != TRUE) {
+                    break;
+                }
 
 #if (BTA_AV_SINK_INCLUDED == TRUE)
                 if (p_data->api_reg.tsep == AVDT_TSEP_SNK) {
@@ -698,7 +711,6 @@ static void bta_av_api_register(tBTA_AV_DATA *p_data)
                     break;
                 }
             }
-#endif
 
             if (!bta_av_cb.reg_audio) {
                 if (p_data->api_reg.tsep == AVDT_TSEP_SRC) {

components/bt/host/bluedroid/bta/include/bta/bta_av_co.h

@@ -87,6 +87,19 @@ typedef struct {
 extern BOOLEAN bta_av_co_audio_init(UINT8 seid, UINT8 *p_codec_type, UINT8 *p_codec_info,
                                     UINT8 *p_num_protect, UINT8 *p_protect_info, UINT8 tsep);
 
+/*******************************************************************************
+**
+** Function         bta_av_co_audio_build_sbc_default
+**
+** Description      Build the mandatory default SBC codec capability for the
+**                  given SEP type (source or sink).
+**
+** Returns          TRUE if built successfully, FALSE otherwise.
+**
+*******************************************************************************/
+extern BOOLEAN bta_av_co_audio_build_sbc_default(UINT8 tsep, UINT8 *p_codec_type,
+                                                 UINT8 *p_codec_info);
+
 /*******************************************************************************
 **
 ** Function         bta_av_co_audio_disc_res

components/bt/host/bluedroid/btc/profile/std/a2dp/bta_av_co.c

@@ -298,6 +298,37 @@ static void bta_av_co_report_peer_all_snk_codec_caps(tBTA_AV_HNDL hndl)
 }
 #endif /* BTC_AV_SRC_INCLUDED */
 
+/*******************************************************************************
+ **
+ ** Function         bta_av_co_audio_build_sbc_default
+ **
+ ** Description      Build the mandatory default SBC codec capability for the
+ **                  given SEP type (source or sink).
+ **
+ ** Returns          TRUE if built successfully, FALSE otherwise.
+ **
+ *******************************************************************************/
+BOOLEAN bta_av_co_audio_build_sbc_default(UINT8 tsep, UINT8 *p_codec_type, UINT8 *p_codec_info)
+{
+    FUNC_TRACE();
+
+    if (p_codec_type == NULL || p_codec_info == NULL) {
+        return FALSE;
+    }
+
+    *p_codec_type = BTA_AV_CODEC_SBC;
+    if (tsep == AVDT_TSEP_SRC) {
+        return (A2D_BldSbcInfo(AVDT_MEDIA_AUDIO, (tA2D_SBC_CIE *)&bta_av_co_sbc_caps,
+                               p_codec_info) == A2D_SUCCESS);
+    } else if (tsep == AVDT_TSEP_SNK) {
+        return (A2D_BldSbcInfo(AVDT_MEDIA_AUDIO, (tA2D_SBC_CIE *)&bta_av_co_sbc_sink_caps,
+                               p_codec_info) == A2D_SUCCESS);
+    }
+
+    APPL_TRACE_WARNING("bta_av_co_audio_build_sbc_default invalid SEP type %d", tsep);
+    return FALSE;
+}
+
 /*******************************************************************************
  **
  ** Function         bta_av_co_audio_init

components/bt/host/bluedroid/btc/profile/std/a2dp/btc_av.c

@@ -1242,9 +1242,15 @@ static bt_status_t btc_av_init(int service_id)
 
 #if (BTC_AV_EXT_CODEC == TRUE)
     UINT8 index;
+    UINT8 tsep = (service_id == BTA_A2DP_SINK_SERVICE_ID) ? AVDT_TSEP_SNK : AVDT_TSEP_SRC;
     for (index = 0; index < BTA_AV_MAX_SEPS; index++) {
-        btc_av_cb.codec_caps[index].id = BTC_AV_CODEC_NONE;
+        /* A2DP mandates SBC: fill every SEID with the default SBC capability */
-        memset(btc_av_cb.codec_caps[index].info, 0, AVDT_CODEC_SIZE);
+        if (bta_av_co_audio_build_sbc_default(tsep, &btc_av_cb.codec_caps[index].id,
+                                              btc_av_cb.codec_caps[index].info) != TRUE) {
+            BTC_TRACE_ERROR("%s: failed to build default SBC for seid %d", __func__, index);
+            btc_av_cb.codec_caps[index].id = BTC_AV_CODEC_NONE;
+            memset(btc_av_cb.codec_caps[index].info, 0, AVDT_CODEC_SIZE);
+        }
     }
 #endif
 
@@ -1629,6 +1635,7 @@ static void btc_av_reg_sep(uint8_t tsep, uint8_t seid, esp_a2d_mcc_t *mcc)
     tBTA_AV_DATA_CBACK *p_data_cback = NULL;
     esp_a2d_cb_param_t param;
     tBTA_AV_CODEC codec_type = ESP_A2D_MCT_NON_A2DP;
+    UINT8 index;
 
     param.a2d_sep_reg_stat.seid = seid;
     if (btc_av_cb.sm_handle == NULL || btc_sm_get_state(btc_av_cb.sm_handle) != BTC_AV_STATE_IDLE) {
@@ -1638,6 +1645,27 @@ static void btc_av_reg_sep(uint8_t tsep, uint8_t seid, esp_a2d_mcc_t *mcc)
         return;
     }
 
+    /*
+     * A2DP requires at least one SBC SEP. Reject a non-SBC registration that
+     * would overwrite the last remaining SBC capability.
+     */
+    if (mcc->type != ESP_A2D_MCT_SBC) {
+        BOOLEAN has_other_sbc = FALSE;
+        for (index = 0; index < BTA_AV_MAX_SEPS; index++) {
+            if (index != seid && btc_av_cb.codec_caps[index].id == BTC_AV_CODEC_SBC) {
+                has_other_sbc = TRUE;
+                break;
+            }
+        }
+        if (!has_other_sbc) {
+            param.a2d_sep_reg_stat.reg_state = ESP_A2D_SEP_REG_SBC_REQUIRED;
+            btc_a2d_cb_to_app(ESP_A2D_SEP_REG_STATE_EVT, &param);
+            BTC_TRACE_WARNING("%s: refuse seid %d codec 0x%02x, at least one SBC SEP is required",
+                              __func__, seid, mcc->type);
+            return;
+        }
+    }
+
     if (tsep == AVDT_TSEP_SNK) {
         p_data_cback = bte_av_media_sink_callback;
     }