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# kCMSampleBufferAttachmentKey_SampleReferenceByteOffset

Indicates the byte offset at which the sample data begins (type `CFNumber`).

```
let kCMSampleBufferAttachmentKey_SampleReferenceByteOffset: CFString
```

## Discussion

This key is only used for sample buffers representing sample references. Its value is the byte offset from the beginning of data at the referenced URL to the contiguous sample data.

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