---
title: transportStateProc
framework: audiotoolbox
role: symbol
role_heading: Instance Property
path: audiotoolbox/hostcallbackinfo/transportstateproc
---

# transportStateProc

Your callback function that provides audio transport state information (play, rewind, and so on) to an audio unit. May be NULL.

## Declaration

```swift
var transportStateProc: HostCallback_GetTransportState?
```