# AudioFile_ReadProc Reads audio data when used in conjunction with the [`AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)) or [`AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:)) functions.) ``` typealias AudioFile_ReadProc = (UnsafeMutableRawPointer, Int64, UInt32, UnsafeMutableRawPointer, UnsafeMutablePointer) -> OSStatus ``` ## Parameters `inClientData` A pointer to the client data as set in the `inClientData` parameter to [`AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileOpenWithCallbacks(_:_:_:_:_:_:_:)) or [`AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileInitializeWithCallbacks(_:_:_:_:_:_:_:_:_:)). `inPosition` An offset into the data from which to read. `requestCount` The number of bytes to read. `buffer` A pointer to the buffer in which to put the data read. `actualCount` On output, the callback should set this parameter to a pointer to the number of bytes successfully read. ## Return Value A result code. See Result Codes. ## Discussion If you named your function `MyAudioFile_ReadProc`, you would declare it like this: ### Discussion This callback function is called when Audio File Services needs to read data. --- 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)