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# AudioQueueTimelineRef

Defines an opaque data type that represents an audio queue timeline object.

```
typealias AudioQueueTimelineRef = OpaquePointer
```

## Discussion

You can use a timeline object to observe time discontinuities in the audio hardware device associated with an audio queue. A discontinuity is, for example, a period of silence when sound was expected. Causes of discontinuities include changes in device state or data processing overloads. See Technical Q&A 1467, [CoreAudio Overload Warnings](https://developer.apple.com/library/archive/qa/qa1467/_index.html#//apple_ref/doc/uid/DTS10003908). You query a timeline object by passing it as a parameter to the [`AudioQueueGetCurrentTime(_:_:_:_:)`](/documentation/AudioToolbox/AudioQueueGetCurrentTime(_:_:_:_:)) function.

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