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# spatialAudioChannelLayoutTag

The audio channel layout tag of the audio sample buffers produced by the audio data output.

```
var spatialAudioChannelLayoutTag: AudioChannelLayoutTag { get set }
```

## Discussion

When you set your audio data output’s associated [`multichannelAudioMode`](/documentation/AVFoundation/AVCaptureDeviceInput/multichannelAudioMode) property to `AVCaptureMultichannelAudioModeFirstOrderAmbisonics`, the [`AVCaptureSession`](/documentation/AVFoundation/AVCaptureSession) allows up to two [`AVCaptureAudioDataOutput`](/documentation/AVFoundation/AVCaptureAudioDataOutput) instances to be connected to the First-order Ambisonsics (FOA) input. If you connect a single [`AVCaptureAudioDataOutput`](/documentation/AVFoundation/AVCaptureAudioDataOutput) instance, you must configure its [`spatialAudioChannelLayoutTag`](/documentation/AVFoundation/AVCaptureAudioDataOutput/spatialAudioChannelLayoutTag) property to produce either four channels of FOA audio or two channels of Stereo audio. If you connect two [`AVCaptureAudioDataOutput`](/documentation/AVFoundation/AVCaptureAudioDataOutput) instances, you must configure one to output four channels of FOA audio and the other to output two channels of Stereo audio.

Thus, when you set your associated [`multichannelAudioMode`](/documentation/AVFoundation/AVCaptureDeviceInput/multichannelAudioMode) property to `AVCaptureMultichannelAudioModeFirstOrderAmbisonics`, you must set your connected [`AVCaptureAudioDataOutput`](/documentation/AVFoundation/AVCaptureAudioDataOutput) instance’s [`spatialAudioChannelLayoutTag`](/documentation/AVFoundation/AVCaptureAudioDataOutput/spatialAudioChannelLayoutTag) property to either `kAudioChannelLayoutTag_Stereo` for stereo, or `(kAudioChannelLayoutTag_HOA_ACN_SN3D | 4)` for FOA (see <doc://com.apple.documentation/documentation/CoreAudioTypes/AudioChannelLayoutTag>). When you set your associated [`multichannelAudioMode`](/documentation/AVFoundation/AVCaptureDeviceInput/multichannelAudioMode) to any other value, the [`AVCaptureSession`](/documentation/AVFoundation/AVCaptureSession) only supports one [`AVCaptureAudioDataOutput`](/documentation/AVFoundation/AVCaptureAudioDataOutput), and you may only set [`spatialAudioChannelLayoutTag`](/documentation/AVFoundation/AVCaptureAudioDataOutput/spatialAudioChannelLayoutTag) to `kAudioChannelLayoutTag_Unknown` (the default value).

Your [`AVCaptureSession`](/documentation/AVFoundation/AVCaptureSession) validates your app’s adherence to the the above rules when you call `AVCaptureSession/startRunning:` or [`commitConfiguration()`](/documentation/AVFoundation/AVCaptureSession/commitConfiguration()) and throws a `NSInvalidArgumentException` if necessary.

---

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