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# transitionToItem(withIdentifier:proposingInitialTimingBasedOn:)

Tells the coordinator to transition to a new item.

```
func transitionToItem(withIdentifier itemIdentifier: String?, proposingInitialTimingBasedOn snapshotTimebase: CMTimebase?)
```

## Parameters

`itemIdentifier`

The identifier for the new current item, which is `nil` if there isn’t anything to play.

`snapshotTimebase`

A time base that communicates the initial playback state of the new item. If you specify `nil`, the coordinator assumes that the player pauses at <doc://com.apple.documentation/documentation/CoreMedia/CMTime/zero>.

    You can retrieve an appropriate time base to pass for this value from AVFoundation playback objects like [`AVSampleBufferRenderSynchronizer`](/documentation/AVFoundation/AVSampleBufferRenderSynchronizer)    . You can also create one manually using the     <doc://com.apple.documentation/documentation/CoreMedia/CMTimebaseCreateWithSourceClock(allocator:sourceClock:timebaseOut:)>     function.

## Discussion

---

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