本文主要是介绍A2DP Source如何从android系统拿到音频数据，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！
Android 13
简单来说就是两条本地socket通道，分别使用文件：
#define A2DP_CTRL_PATH "/data/misc/bluedroid/.a2dp_ctrl"
#define A2DP_DATA_PATH "/data/misc/bluedroid/.a2dp_data"
A2DP_CTRL_PATH是控制通道，A2DP_DATA_PATH是数据通道。
packages\modules\Bluetooth\system\audio_a2dp_hw\include\audio_a2dp_hw.h
1、首先需要关注一个文件 btif_a2dp_control.cc
// packages\modules\Bluetooth\system\btif\src\btif_a2dp_control.cc
void btif_a2dp_control_init(void) {a2dp_uipc = UIPC_Init();UIPC_Open(*a2dp_uipc, UIPC_CH_ID_AV_CTRL, btif_a2dp_ctrl_cb, A2DP_CTRL_PATH);
}里面的函数UIPC_Init
// packages\modules\Bluetooth\system\udrv\ulinux\uipc.ccstd::unique_ptr<tUIPC_STATE> UIPC_Init() {std::unique_ptr<tUIPC_STATE> uipc = std::make_unique<tUIPC_STATE>();LOG_DEBUG("UIPC_Init");std::lock_guard<std::recursive_mutex> lock(uipc->mutex);uipc_main_init(*uipc);uipc_start_main_server_thread(*uipc);return uipc;
}初始化一些uipc的变量，然后启动主线程uipc_read_task
int uipc_start_main_server_thread(tUIPC_STATE& uipc) {uipc.running = 1;if (pthread_create(&uipc.tid, (const pthread_attr_t*)NULL, uipc_read_task,&uipc) != 0) {LOG_ERROR("uipc_thread_create pthread_create failed:%d", errno);return -1;}return 0;
}这里面的实现不太需要关注。
2、UIPC_Open(UIPC_CH_ID_AV_CTRL, btif_a2dp_ctrl_cb);启动控制通道。注册回调btif_a2dp_ctrl_cb
packages\modules\Bluetooth\system\btif\src\btif_a2dp_control.cc
static void btif_a2dp_ctrl_cb(UNUSED_ATTR tUIPC_CH_ID ch_id,tUIPC_EVENT event) {// Don't log UIPC_RX_DATA_READY_EVT by default, because it// could be very chatty when audio is streaming.if (event == UIPC_RX_DATA_READY_EVT) {APPL_TRACE_DEBUG("%s: A2DP-CTRL-CHANNEL EVENT %s", __func__,dump_uipc_event(event));} else {APPL_TRACE_WARNING("%s: A2DP-CTRL-CHANNEL EVENT %s", __func__,dump_uipc_event(event));}switch (event) {case UIPC_OPEN_EVT:break;case UIPC_CLOSE_EVT:/* restart ctrl server unless we are shutting down */if (btif_a2dp_source_media_task_is_running())UIPC_Open(*a2dp_uipc, UIPC_CH_ID_AV_CTRL, btif_a2dp_ctrl_cb,A2DP_CTRL_PATH);break;case UIPC_RX_DATA_READY_EVT:btif_a2dp_recv_ctrl_data();break;default:APPL_TRACE_ERROR("%s: ### A2DP-CTRL-CHANNEL EVENT %d NOT HANDLED ###",__func__, event);break;}
}3、btif_a2dp_recv_ctrl_data(); 这个函数就是处理收到的控制指令，例如get configure，set configure、stream start、stream suspend等。
4、当收到stream start的时候就会启动数据通道
static void btif_a2dp_recv_ctrl_data(void) {tA2DP_CTRL_CMD cmd = A2DP_CTRL_CMD_NONE;int n;...a2dp_cmd_pending = cmd;switch (cmd) {...case A2DP_CTRL_CMD_START:btif_a2dp_command_ack(btif_a2dp_control_on_start());break;...
}
static tA2DP_CTRL_ACK btif_a2dp_control_on_start() {/** Don't send START request to stack while we are in a call.* Some headsets such as "Sony MW600", don't allow AVDTP START* while in a call, and respond with BAD_STATE.*/if (!bluetooth::headset::IsCallIdle()) {APPL_TRACE_WARNING("%s: A2DP command start while call state is busy",__func__);return A2DP_CTRL_ACK_INCALL_FAILURE;}if (btif_a2dp_source_is_streaming()) {APPL_TRACE_WARNING("%s: A2DP command start while source is streaming",__func__);return A2DP_CTRL_ACK_FAILURE;}if (btif_av_stream_ready()) {/* Setup audio data channel listener */UIPC_Open(*a2dp_uipc, UIPC_CH_ID_AV_AUDIO, btif_a2dp_data_cb,A2DP_DATA_PATH);/** Post start event and wait for audio path to open.* If we are the source, the ACK will be sent after the start* procedure is completed, othewise send it now.*/btif_av_stream_start();if (btif_av_get_peer_sep() == AVDT_TSEP_SRC) return A2DP_CTRL_ACK_SUCCESS;}if (btif_av_stream_started_ready()) {/** Already started, setup audio data channel listener and ACK* back immediately.*/UIPC_Open(*a2dp_uipc, UIPC_CH_ID_AV_AUDIO, btif_a2dp_data_cb,A2DP_DATA_PATH);return A2DP_CTRL_ACK_SUCCESS;}APPL_TRACE_WARNING("%s: A2DP command start while AV stream is not ready",__func__);return A2DP_CTRL_ACK_FAILURE;
}
5、启动数据通道后，会通过回调btif_a2dp_data_cb通知，进行一些必要的操作后（具体参考原生代码btif_a2dp_data_cb的实现），就可以使用UIPC_Read(UIPC_CH_ID_AV_AUDIO, &event, p_buf, len);读取到数据了。这里如果要使用自己的蓝牙可以建立线程读取数据，当stream stop或者stream suspend时cancel掉线程即可
6、注意：如果静音模式audio manager不会向控制发送stream start，所以如果其他指令都收到了没有收到stream start可以调节下声音试试。
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