---
title: transportStateBlock
framework: audiotoolbox
role: symbol
role_heading: Instance Property
path: audiotoolbox/auaudiounit/transportstateblock
---

# transportStateBlock

A callback to the host for transport state information.

## Declaration

```swift
var transportStateBlock: AUHostTransportStateBlock? { get set }
```

## Discussion

Discussion An audio unit accessing this property should cache it in realtime-safe storage before beginning to render. This version 3 property is bridged to the version 2 HostCallback_GetTransportState and HostCallback_GetTransportState2 callback members in the kAudioUnitProperty_HostCallbacks API.

## See Also

### Providing Data to the Host

- [musicalContextBlock](audiotoolbox/auaudiounit/musicalcontextblock.md)
- [contextName](audiotoolbox/auaudiounit/contextname.md)
- [supportsMPE](audiotoolbox/auaudiounit/supportsmpe.md)
- [AUHostMusicalContextBlock](audiotoolbox/auhostmusicalcontextblock.md)
- [AUHostTransportStateBlock](audiotoolbox/auhosttransportstateblock.md)