# AUInputHandler A block to notify the host of an I/O unit that an input is available. ``` typealias AUInputHandler = (UnsafeMutablePointer, UnsafePointer, AUAudioFrameCount, Int) -> Void ``` ## Discussion The block takes the following parameters: - actionFlags: The pointer to the action flags. - timestamp: The HAL time at which the input data will be rendered. If there is a sample rate conversion or time compression/expansion downstream, the sample time will not be valid. - frameCount: The number of sample frames of input available. - inputBusNumber: The index of the input bus from which input is available. The input data is obtained by calling the render block of the audio unit. The audio unit is not provided since it is not safe to message an Objective-C object in a real-time context. --- Copyright © 2026 Apple Inc. All rights reserved. | [Terms of Use](https://www.apple.com/legal/internet-services/terms/site.html) | [Privacy Policy](https://www.apple.com/privacy/privacy-policy)