---
title: trimDurationAtStart
framework: coremedia
role: symbol
role_heading: Type Property
path: coremedia/cmsamplebufferattachmentkeydefinitions/trimdurationatstart
---

# trimDurationAtStart

The duration that should be removed at the beginning of the sample buffer, after decoding.

## Declaration

```swift
static let trimDurationAtStart: CVAttachmentKeyDefinitionWithDefault<CMSampleBufferAttachmentKeyDefinitions.ShouldPropagate, CMTime>
```

## Discussion

Discussion The getter returns the default value of zero (nothing removed) if this attachment is not present. In cases where all the output after decoding the sample buffer is to be discarded (for example, the samples are only being decoded to prime the decoder) the usual convention is to set trimDurationAtStart to the whole duration and not to set a trimDurationAtEnd attachment.