# AudioFileStream_PacketsProc Invoked by an audio file stream parser when it finds audio data in the audio file stream. ``` typealias AudioFileStream_PacketsProc = (UnsafeMutableRawPointer, UInt32, UInt32, UnsafeRawPointer, UnsafeMutablePointer?) -> Void ``` ## Parameters `inClientData` The value you provided in the `inClientData` parameter when you called the [`AudioFileStreamOpen(_:_:_:_:_:)`](/documentation/AudioToolbox/AudioFileStreamOpen(_:_:_:_:_:)) function. `inNumberBytes` The number of bytes of data in the `inInputData` buffer. `inNumberPackets` The number of packets of audio data in the `inInputData` buffer. `inInputData` The audio data. `inPacketDescriptions` An array of audio file stream packet description structures describing the data. Audio file stream packet description structures are described in . ## Discussion If you named your function `MyAudioFileStream_PacketsProc`, you would declare it like this: ### Discussion For constant-bit-rate (CBR) audio data, your callback is typically called with as much data as you passed to the [`AudioFileStreamParseBytes(_:_:_:_:)`](/documentation/AudioToolbox/AudioFileStreamParseBytes(_:_:_:_:)) function. At times, however, only a single packet might be passed because of boundaries in the input data. For variable-bit-rate (VBR) audio data, your callback might be called several times for each time you called the [`AudioFileStreamParseBytes(_:_:_:_:)`](/documentation/AudioToolbox/AudioFileStreamParseBytes(_:_:_:_:)) function. --- 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)