# AudioQueuePropertyID Identifiers for audio queue properties. ``` typealias AudioQueuePropertyID = UInt32 ``` ## Discussion To receive a notification that a specific audio queue property has changed: 1. Define a property listener callback, referencing the desired audio queue property ID. Base the callback on the [`AudioQueuePropertyListenerProc`](/documentation/AudioToolbox/AudioQueuePropertyListenerProc) callback function declaration. 2. Assign the callback to an audio queue using the [`AudioQueueAddPropertyListener(_:_:_:_:)`](/documentation/AudioToolbox/AudioQueueAddPropertyListener(_:_:_:_:)) function. 3. When you get a property-changed notification, call the [`AudioQueueGetProperty(_:_:_:_:)`](/documentation/AudioToolbox/AudioQueueGetProperty(_:_:_:_:)) function to get the current value of the property. ## Topics ### Constants [`kAudioQueueProperty_IsRunning`](/documentation/AudioToolbox/kAudioQueueProperty_IsRunning) Value is a read-only `UInt32` value indicating whether or not the audio queue is running. A nonzero value means running; `0` means stopped. A notification is sent when the associated audio queue starts or stops, which may occur sometime after the [`AudioQueueStart(_:_:)`](/documentation/AudioToolbox/AudioQueueStart(_:_:)) or [`AudioQueueStop(_:_:)`](/documentation/AudioToolbox/AudioQueueStop(_:_:)) function is called. [`kAudioQueueDeviceProperty_SampleRate`](/documentation/AudioToolbox/kAudioQueueDeviceProperty_SampleRate) Value is a read-only `Float64` value representing the sampling rate of the audio hardware device associated with an audio queue. [`kAudioQueueDeviceProperty_NumberChannels`](/documentation/AudioToolbox/kAudioQueueDeviceProperty_NumberChannels) Value is a read-only `UInt32` value representing the number of channels in the audio hardware device associated with an audio queue. [`kAudioQueueProperty_CurrentDevice`](/documentation/AudioToolbox/kAudioQueueProperty_CurrentDevice) The unique identifier (UID) of the audio hardware device. [`kAudioQueueProperty_MagicCookie`](/documentation/AudioToolbox/kAudioQueueProperty_MagicCookie) Value is a read/write void pointer to a block of memory, which you set up, containing an audio format magic cookie. If the audio format you are playing or recording to requires a magic cookie, you must set a value for this property before enqueuing any buffers. [`kAudioQueueProperty_MaximumOutputPacketSize`](/documentation/AudioToolbox/kAudioQueueProperty_MaximumOutputPacketSize) Value is a read-only`UInt32` value that is the size, in bytes, of the largest single packet of data in the output format. Primarily useful when encoding VBR compressed data. [`kAudioQueueProperty_StreamDescription`](/documentation/AudioToolbox/kAudioQueueProperty_StreamDescription) An audio queue’s data format. [`kAudioQueueProperty_ChannelLayout`](/documentation/AudioToolbox/kAudioQueueProperty_ChannelLayout) Describes an audio queue channel layout. [`kAudioQueueProperty_EnableLevelMetering`](/documentation/AudioToolbox/kAudioQueueProperty_EnableLevelMetering) Value is a read/write `UInt32` value that indicates whether audio level metering is enabled for an audio queue. `0` = metering off, `1` = metering on. [`kAudioQueueProperty_CurrentLevelMeter`](/documentation/AudioToolbox/kAudioQueueProperty_CurrentLevelMeter) A read-only array of level meter status structures. [`kAudioQueueProperty_CurrentLevelMeterDB`](/documentation/AudioToolbox/kAudioQueueProperty_CurrentLevelMeterDB) Value is a read-only array of [`AudioQueueLevelMeterState`](/documentation/AudioToolbox/AudioQueueLevelMeterState) structures, one array element per audio channel. The member values in the structure are in decibels. [`kAudioQueueProperty_DecodeBufferSizeFrames`](/documentation/AudioToolbox/kAudioQueueProperty_DecodeBufferSizeFrames) Value is a read/write `UInt32` value that is the size of the buffer into which a playback (output) audio queue decodes buffers. A larger buffer provides more reliability and better long-term performance at the expense of memory and decreased responsiveness in some situations. [`kAudioQueueProperty_ConverterError`](/documentation/AudioToolbox/kAudioQueueProperty_ConverterError) Value is a read-only `UInt32` value that indicates the most recent error (if any) encountered by the audio queue’s internal encoding/decoding process. --- 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)