---
title: kVTEncodeFrameOptionKey_AcknowledgedLTRTokens
framework: videotoolbox
role: symbol
role_heading: Global Variable
path: videotoolbox/kvtencodeframeoptionkey_acknowledgedltrtokens
---

# kVTEncodeFrameOptionKey_AcknowledgedLTRTokens

Enable Long Term Reference (LTR) frames during encoding.

## Declaration

```swift
let kVTEncodeFrameOptionKey_AcknowledgedLTRTokens: CFString
```

## See Also

### Long-Term Reference

- [kVTCompressionPropertyKey_EnableLTR](videotoolbox/kvtcompressionpropertykey_enableltr.md)
- [kVTEncodeFrameOptionKey_ForceLTRRefresh](videotoolbox/kvtencodeframeoptionkey_forceltrrefresh.md)
- [kVTSampleAttachmentKey_RequireLTRAcknowledgementToken](videotoolbox/kvtsampleattachmentkey_requireltracknowledgementtoken.md)