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# kCMSampleBufferAttachmentKey_TransitionID

Marks a transition from one source of buffers to another.

```
let kCMSampleBufferAttachmentKey_TransitionID: CFString
```

## Discussion

For example, during gapless playback of a list of songs, this attachment marks the first buffer from the next song.        If this attachment is on a buffer containing no samples, the first following buffer that contains samples is the        buffer that contains the first samples from the next song.  The value of this attachment is a <doc://com.apple.documentation/documentation/CoreFoundation/CFTypeRef>.  This        transition identifier should be unique within a playlist, so each transition in a playlist is uniquely        identifiable.  A <doc://com.apple.documentation/documentation/CoreFoundation/CFNumber> counter that increments with each transition is a simple example.

---

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