---
title: speedMultiplier
framework: coremedia
role: symbol
role_heading: Type Property
path: coremedia/cmsamplebufferattachmentkeydefinitions/speedmultiplier
---

# speedMultiplier

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

## Declaration

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

## Discussion

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. 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).