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# timebase

The timebase information for the item.

```
nonisolated var timebase: CMTimebase? { get }
```

## Discussion

The system uses timebase information to synchronize playback of the current item with the host clock. You can use this property to access the timebase information, but you can’t use it to set the time or the rate of playback.

If you need to respond to changes in the effective playback rate, listen for <doc://com.apple.documentation/documentation/CoreMedia/kCMTimebaseNotification_EffectiveRateChanged> notifications that the player item’s [`timebase`](/documentation/AVFoundation/AVPlayerItem/timebase) posts. These notifications announce when the effective playback rate changes, which includes any compensation necessary for drifting behaviors of audio output hardware.

---

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