遇到客户一个需求，如果连接了带mic的蓝牙耳机，默认所有的录音要走蓝牙mic通道。

这个功能搞了好久，终于搞定了。

1. 向RK寻求帮助，先打通 bt sco能力。

此时，还无法默认就切换到蓝牙 mic通道，接下来我们需求默认切换到蓝牙通道。

2. 修改frameworks/av/services/audiopolicy/enginedefault/src/Engine.cpp，

默认走bt sco的mic录音输入源     

switch (inputSource) {
case AUDIO_SOURCE_DEFAULT:
case AUDIO_SOURCE_MIC:
device = availableDevices.getDevice(
AUDIO_DEVICE_IN_BLUETOOTH_A2DP, String8(""), AUDIO_FORMAT_DEFAULT);
if (device != nullptr) break;
if (audio_is_bluetooth_out_sco_device(commDeviceType)) {
device = availableDevices.getDevice(
AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET, String8(""), AUDIO_FORMAT_DEFAULT);
if (device != nullptr) break;
}
device = availableDevices.getFirstExistingDevice({
+                AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET,
AUDIO_DEVICE_IN_BLE_HEADSET, AUDIO_DEVICE_IN_WIRED_HEADSET,
AUDIO_DEVICE_IN_USB_HEADSET, AUDIO_DEVICE_IN_USB_DEVICE,
AUDIO_DEVICE_IN_BLUETOOTH_BLE, AUDIO_DEVICE_IN_BUILTIN_MIC});
break;

case AUDIO_SOURCE_CAMCORDER:
// For a device without built-in mic, adding usb device
device = availableDevices.getFirstExistingDevice({
-               AUDIO_DEVICE_IN_USB_DEVICE,
+              AUDIO_DEVICE_IN_BLUETOOTH_SCO_HEADSET, AUDIO_DEVICE_IN_USB_DEVICE,
AUDIO_DEVICE_IN_BACK_MIC, AUDIO_DEVICE_IN_BUILTIN_MIC});
break;
case AUDIO_SOURCE_VOICE_DOWNLINK:

3. 很关键的一步，在一个常驻service里边（或者可以在system ui模块实现）监听插入蓝牙耳机，进行默认sco模式切换

IntentFilter filter = new IntentFilter();
filter.addAction(BluetoothDevice.ACTION_ACL_CONNECTED);
filter.addAction(BluetoothDevice.ACTION_ACL_DISCONNECTED);
registerReceiver(myReceiver, filter);

BroadcastReceiver myReceiver = new BroadcastReceiver() {@Overridepublic void onReceive(Context context, Intent intent) {if (BluetoothDevice.ACTION_ACL_CONNECTED.equals(intent.getAction())) {Log.d("mod@bt", "bt connected");startBluetoothRecording(context);});} else if (BluetoothDevice.ACTION_ACL_DISCONNECTED.equals(intent.getAction())) {Log.d("mod@bt", "bt disconnected");stopRecording(context);}}}
};

    public void startBluetoothRecording(Context context) {
try {
AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);

            if (!audioManager.isBluetoothScoOn()) {
audioManager.setMode(AudioManager.MODE_IN_COMMUNICATION);
audioManager.setBluetoothScoOn(true);
audioManager.startBluetoothSco();
}
} catch (Exception e) {
e.printStackTrace();
}
}

    public void stopRecording(Context context) {
try {

            AudioManager audioManager = (AudioManager) context.getSystemService(Context.AUDIO_SERVICE);

            if (audioManager.isBluetoothScoOn()) {
audioManager.setBluetoothScoOn(false);
audioManager.stopBluetoothSco();

            }

            audioManager.setMode(AudioManager.MODE_NORMAL);
audioManager.setSpeakerphoneOn(true);
} catch (Exception e) {
e.printStackTrace();
}
}

4. 如上操作后，每次即使应用选择了系统默认mic，也会走bt sco通道录音。

5. 当然，可能会遇到其他的优化问题，如果你有需求，欢迎给我留言。