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# speedMultiplier

The factor by which the sample buffer’s presentation should be accelerated.

```
static let speedMultiplier: CVAttachmentKeyDefinitionWithDefault<CMSampleBufferAttachmentKeyDefinitions.ShouldPropagate, Float>
```

## Discussion

For normal playback the speed multiplier would be 1.0 (which is the default value returned by getter if this
attachment is not present); for double-speed playback the speed multiplier would be 2.0, which would halve the
output duration. Speed-multiplication factors take effect after trimming; see
[`outputDuration`](/documentation/CoreMedia/CMReadySampleBuffer/outputDuration). Note that this attachment principally provides information about the
duration-stretching effect: by default, it should be implemented by rate conversion, but other attachments may
specify richer stretching operations—for example, scaling without pitch shift, or pitch shift without changing
duration. Sequences of speed-multiplied sample buffers should have explicit time stamps to clarify when each
should be output (see [`outputPresentationTimeStamp`](/documentation/CoreMedia/CMReadySampleBuffer/outputPresentationTimeStamp)).

---

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