---
title: kCMSampleBufferAttachmentKey_TrimDurationAtStart
framework: coremedia
role: symbol
role_heading: Global Variable
path: coremedia/kcmsamplebufferattachmentkey_trimdurationatstart
---

# kCMSampleBufferAttachmentKey_TrimDurationAtStart

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

## Declaration

```swift
let kCMSampleBufferAttachmentKey_TrimDurationAtStart: CFString
```

## Discussion

Discussion If this attachment is not present, the trim duration is zero (nothing removed).        This is a CMTime in Core Foundation dictionary format as made by CMTimeCopyAsDictionary(_:allocator:);         use CMTimeMakeFromDictionary(_:) to convert to CMTime.        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 kCMSampleBufferAttachmentKey_TrimDurationAtStart to the whole duration         and not to set a kCMSampleBufferAttachmentKey_TrimDurationAtEnd attachment.

## See Also

### Sample Buffer Keys

- [kCMSampleBufferAttachmentKey_DisplayEmptyMediaImmediately](coremedia/kcmsamplebufferattachmentkey_displayemptymediaimmediately.md)
- [kCMSampleBufferAttachmentKey_DrainAfterDecoding](coremedia/kcmsamplebufferattachmentkey_drainafterdecoding.md)
- [kCMSampleBufferAttachmentKey_DroppedFrameReason](coremedia/kcmsamplebufferattachmentkey_droppedframereason.md)
- [kCMSampleBufferDroppedFrameReason_FrameWasLate](coremedia/kcmsamplebufferdroppedframereason_framewaslate.md)
- [kCMSampleBufferDroppedFrameReason_OutOfBuffers](coremedia/kcmsamplebufferdroppedframereason_outofbuffers.md)
- [kCMSampleBufferDroppedFrameReason_Discontinuity](coremedia/kcmsamplebufferdroppedframereason_discontinuity.md)
- [kCMSampleBufferAttachmentKey_DroppedFrameReasonInfo](coremedia/kcmsamplebufferattachmentkey_droppedframereasoninfo.md)
- [kCMSampleBufferDroppedFrameReasonInfo_CameraModeSwitch](coremedia/kcmsamplebufferdroppedframereasoninfo_cameramodeswitch.md)
- [kCMSampleBufferAttachmentKey_EmptyMedia](coremedia/kcmsamplebufferattachmentkey_emptymedia.md)
- [kCMSampleBufferAttachmentKey_EndsPreviousSampleDuration](coremedia/kcmsamplebufferattachmentkey_endsprevioussampleduration.md)
- [kCMSampleBufferAttachmentKey_FillDiscontinuitiesWithSilence](coremedia/kcmsamplebufferattachmentkey_filldiscontinuitieswithsilence.md)
- [kCMSampleBufferAttachmentKey_ForceKeyFrame](coremedia/kcmsamplebufferattachmentkey_forcekeyframe.md)
- [kCMSampleBufferAttachmentKey_GradualDecoderRefresh](coremedia/kcmsamplebufferattachmentkey_gradualdecoderrefresh.md)
- [kCMSampleBufferAttachmentKey_PermanentEmptyMedia](coremedia/kcmsamplebufferattachmentkey_permanentemptymedia.md)
- [kCMSampleBufferAttachmentKey_PostNotificationWhenConsumed](coremedia/kcmsamplebufferattachmentkey_postnotificationwhenconsumed.md)