# Audio Output Device Management (ArkTS)

If a device is connected to multiple audio output devices, you can use **AudioRoutingManager** to specify an audio output device to play audio. For details about the API reference, see [AudioRoutingManager](../reference/apis-audio-kit/js-apis-audio.md#audioroutingmanager9).

## Creating an AudioRoutingManager Instance

Before using **AudioRoutingManager** to manage audio devices, import the audio module and create an **AudioManager** instance.

```ts
import audio from '@ohos.multimedia.audio'; // Import the audio module.

let audioManager = audio.getAudioManager(); // Create an AudioManager instance.

let audioRoutingManager = audioManager.getRoutingManager(); // Call an API of AudioManager to create an AudioRoutingManager instance.
```

## Supported Audio Output Device Types

The table below lists the supported audio output devices.

| Name| Value| Description| 
| -------- | -------- | -------- |
| EARPIECE | 1 | Earpiece.| 
| SPEAKER | 2 | Speaker.| 
| WIRED_HEADSET | 3 | Wired headset with a microphone.| 
| WIRED_HEADPHONES | 4 | Wired headset without microphone.| 
| BLUETOOTH_SCO | 7 | Bluetooth device using Synchronous Connection Oriented (SCO) links.| 
| BLUETOOTH_A2DP | 8 | Bluetooth device using Advanced Audio Distribution Profile (A2DP) links.| 
| USB_HEADSET | 22 | USB Type-C headset.| 

## Obtaining Output Device Information

Use **getDevices()** to obtain information about all the output devices.

```ts
import audio from '@ohos.multimedia.audio';

audioRoutingManager.getDevices(audio.DeviceFlag.OUTPUT_DEVICES_FLAG).then((data: audio.AudioDeviceDescriptors) => {
  console.info('Promise returned to indicate that the device list is obtained.');
});
```

## Listening for Device Connection State Changes

Set a listener to listen for changes of the device connection state. When a device is connected or disconnected, a callback is triggered.

```ts
import audio from '@ohos.multimedia.audio';

// Listen for connection state changes of audio devices.
audioRoutingManager.on('deviceChange', audio.DeviceFlag.OUTPUT_DEVICES_FLAG, (deviceChanged: audio.DeviceChangeAction) => {
  console.info(`device change type : ${deviceChanged.type}`);  // Device connection state change. The value 0 means that the device is connected and 1 means that the device is disconnected.
  console.info(`device descriptor size : ${deviceChanged.deviceDescriptors.length}`);
  console.info(`device change descriptor : ${deviceChanged.deviceDescriptors[0].deviceRole}`);  // Device role.
  console.info(`device change descriptor : ${deviceChanged.deviceDescriptors[0].deviceType}`);  // Device type.
});

// Cancel the listener for the connection state changes of audio devices.
audioRoutingManager.off('deviceChange');
```

## Selecting an Audio Output Device (for System Applications only)

Currently, only one output device can be selected, and the device ID is used as the unique identifier. For details about audio device descriptors, see [AudioDeviceDescriptors](../reference/apis-audio-kit/js-apis-audio.md#audiodevicedescriptors).

> **NOTE**
> 
> The user can connect to a group of audio devices (for example, a pair of Bluetooth headsets), but the system treats them as one device (a group of devices that share the same device ID).

```ts
import audio from '@ohos.multimedia.audio';
import { BusinessError } from '@ohos.base';

let outputAudioDeviceDescriptor: audio.AudioDeviceDescriptors = [{
    deviceRole : audio.DeviceRole.OUTPUT_DEVICE,
    deviceType : audio.DeviceType.SPEAKER,
    id : 1,
    name : "",
    address : "",
    sampleRates : [44100],
    channelCounts : [2],
    channelMasks : [0],
    networkId : audio.LOCAL_NETWORK_ID,
    interruptGroupId : 1,
    volumeGroupId : 1,
    displayName : ""
}];

async function selectOutputDevice() {
  audioRoutingManager.selectOutputDevice(outputAudioDeviceDescriptor).then(() => {
    console.info('Invoke selectOutputDevice succeeded.');
  }).catch((err: BusinessError) => {
    console.error(`Invoke selectOutputDevice failed, code is ${err.code}, message is ${err.message}`);
  });
}
```

## Obtaining Information About the Output Device with the Highest Priority

Call **getPreferOutputDeviceForRendererInfo()** to obtain the output device with the highest priority.

> **NOTE**
>
> The output device with the highest priority is the device that will output audio.

```ts
import audio from '@ohos.multimedia.audio';
import { BusinessError } from '@ohos.base';

let rendererInfo: audio.AudioRendererInfo = {
    usage : audio.StreamUsage.STREAM_USAGE_MUSIC,
    rendererFlags : 0
}

async function getPreferOutputDeviceForRendererInfo() {
  audioRoutingManager.getPreferOutputDeviceForRendererInfo(rendererInfo).then((desc: audio.AudioDeviceDescriptors) => {
    console.info(`device descriptor: ${desc}`);
  }).catch((err: BusinessError) => {
    console.error(`Result ERROR: ${err}`);
  })
}
```

## Listening for Changes of the Output Device with the Highest Priority

```ts
import audio from '@ohos.multimedia.audio';

let rendererInfo: audio.AudioRendererInfo = {
    usage : audio.StreamUsage.STREAM_USAGE_MUSIC,
    rendererFlags : 0
}

// Listen for changes of the output device with the highest priority.
audioRoutingManager.on('preferOutputDeviceChangeForRendererInfo', rendererInfo, (desc: audio.AudioDeviceDescriptors) => {
    console.info(`device change descriptor : ${desc[0].deviceRole}`);  // Device role.
    console.info(`device change descriptor : ${desc[0].deviceType}`);  // Device type.
});

// Cancel the listening for changes of the output device with the highest priority.
audioRoutingManager.off('preferOutputDeviceChangeForRendererInfo');
```