---
title: sourceFormatHint
framework: avfoundation
role: symbol
role_heading: Instance Property
path: avfoundation/avassetwriterinput/sourceformathint
---

# sourceFormatHint

A hint about the format of the sample buffers to append to the input.

## Declaration

```swift
var sourceFormatHint: CMFormatDescription? { get }
```

## Discussion

Discussion An input may use this hint to fill in missing output settings or perform additional upfront validation of samples. note: To ensure successful file writing when you initialize an input with a source format hint, only append samples of this type.

## See Also

### Inspecting an input

- [mediaType](avfoundation/avassetwriterinput/mediatype.md)
- [outputSettings](avfoundation/avassetwriterinput/outputsettings.md)