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# transitionID

Marks a transition from one source of buffers to another.

```
static let transitionID: CVAttachmentKeyDefinition<CMSampleBufferAttachmentKeyDefinitions.ShouldNotPropagate, Int>
```

## Discussion

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. This transition identifier should be unique within a
playlist, so each transition in a playlist is uniquely identifiable. A counter that increments with each
transition is a simple example.

---

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