---
title: sampleReferenceBaseURL
framework: avfoundation
role: symbol
role_heading: Instance Property
path: avfoundation/avassetwriterinput/samplereferencebaseurl
---

# sampleReferenceBaseURL

The base URL sample references are relative to.

## Declaration

```swift
var sampleReferenceBaseURL: URL? { get set }
```

## Discussion

Discussion This property is only valid for file types that support writing sample references, such as QuickTime files. If the system resolves the value of this property to an absolute URL, the sample references it appends are relative to this URL. The URL must point to a location that’s in a directory that’s a parent of the sample reference location. For example, setting the value of this property to file:///User/johnappleseed/Movies/ and appending sample buffers with the kCMSampleBufferAttachmentKey_SampleReferenceURL attachment set to file:///User/johnappleseed/Movies/data/movie1.mov writes a sample reference of data/movie1.mov to the movie.

## See Also

### Configuring media data layout

- [preferredMediaChunkAlignment](avfoundation/avassetwriterinput/preferredmediachunkalignment.md)
- [preferredMediaChunkDuration](avfoundation/avassetwriterinput/preferredmediachunkduration.md)
- [mediaDataLocation](avfoundation/avassetwriterinput/mediadatalocation-swift.property.md)
- [AVAssetWriterInput.MediaDataLocation](avfoundation/avassetwriterinput/mediadatalocation-swift.struct.md)