Dive into the technical aspects of audio on your device, including codecs, format support, and customization options.

Audio Documentation

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Audio player app is silent if device connected via CarPlay
I have a SwiftUI app - (https://youtu.be/VbAfUk_eYl0?si=JxUBh0Bpb-vc1E1U) - which I thought was almost ready for release - a manager for airdropped audio files from Logic Pro or other music creation applications. It uses AVAudioEngine and AVAudioPlayerNode to play audio, and the MediaPlayer API to integrate with car audio and similar, all of which works well. It does not currently have an explicit CarPlay integration (and I'm slightly horrified at the amount of work that is going to require). I had the good or bad luck of getting a loaner car with carplay while mine is being repaired yesterday, and lo and behold, when connected to the vehicle via CarPlay, there is no audio output in the vehicle at all. The now playing panel correctly shows the information my app provides about the currently playing song; the player node believes it is playing, the AVAudioSession is configured as it should be. But there is no sound. Obviously I cannot ship it in this state. I've tried fiddling with the parameters the AVAudioSession is configured with, in case there was some parameter that was preventing audio output, to no avail - currently: var options = AVAudioSession.CategoryOptions() options.insert(.allowAirPlay) options.insert(.allowBluetooth) options.insert(.allowBluetoothA2DP) try session.setCategory(.playback, mode: .default, options: options) try? session.setPreferredIOBufferDuration(0.002) // ~96 samples at 44.1kHz try? session.setPrefersNoInterruptionsFromSystemAlerts(true) try? session.setPrefersInterruptionOnRouteDisconnect(false) try session.setActive(true, options: [.notifyOthersOnDeactivation]) All diagnostics within the app show the player operating correctly - files are played and flushed; AVAudioPlayerNodeCompletionCallbacks are called when they should be. But the output is not audible in the vehicle. I would much prefer to ship this app without full-blown CarPlay integration, but with working audio when connected via CarPlay, and work on full CarPlay integration for the next release. Is there some secret handshake I am just missing to make this work?
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235
Mar ’25
USB microphone input : Mac "Designed for iPad"
My app - natively iOS but built with the "Designed for iPad" option to run on Mac - does not recognise an attached USB microphone when running on a Mac. This line int32_t items = (int32_t) [[[AVAudioSession sharedInstance] availableInputs] count ]; returns 1, which is the Mac internal mic. On iPad and iPhone it sees both the internal mic and the USB mic. Is this an inherent "Designed for iPad" restriction, and is there some trick I can pull to get the USB microphone to be recognised by the system?
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268
Jan ’26
Where is the License Agreement for Android version of ShazamKit?
I have integrated the ShazamKit SDK into my iOS app and would like to implement the same functionality in my Android app. My question is: Can I use the Android version of the ShazamKit SDK for commercial purposes? After extensive research, I could not find any official information regarding the license of the Android version of the ShazamKit SDK. Could you please provide a formal license statement?
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142
Apr ’25
[AVPlayerItemVideoOutput initWithPixelBufferAttributes:] output attributes setting not work
My app want Converting iphone12 HDR Video to SDR,to edit。 follow the doc Apple-HDR-Convert. My code setting the pixBuffAttributes        [pixBuffAttributes setObject:(id)(kCVImageBufferYCbCrMatrix_ITU_R_709_2) forKey:(id)kCVImageBufferYCbCrMatrixKey];       [pixBuffAttributes setObject:(id)(kCVImageBufferColorPrimaries_ITU_R_709_2) forKey:(id)kCVImageBufferColorPrimariesKey];       [pixBuffAttributes setObject:(id)kCVImageBufferTransferFunction_ITU_R_709_2 forKey:(id)kCVImageBufferTransferFunctionKey];       playerItemOutput = [[AVPlayerItemVideoOutput alloc] initWithPixelBufferAttributes:pixBuffAttributes]; but I get the playerItemOutput's output buffer   CFTypeRef colorAttachments = CVBufferGetAttachment(pixelBuffer, kCVImageBufferYCbCrMatrixKey, NULL);     CFTypeRef colorPrimaries = CVBufferGetAttachment(pixelBuffer, kCVImageBufferColorPrimariesKey, NULL);     CFTypeRef colorTransFunc = CVBufferGetAttachment(pixelBuffer, kCVImageBufferTransferFunctionKey, NULL);      NSLog(@"colorAttachments = %@", colorAttachments);     NSLog(@"colorPrimaries = %@", colorPrimaries);     NSLog(@"colorTransFunc = %@", colorTransFunc); log output: colorAttachments = ITU_R_2020 colorPrimaries = ITU_R_2020 colorTransFunc = ITU_R_2100_HLG pixBuffAttributes setting output format invalid,please help!
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838
Nov ’25
AudioOutputUnitStart takes ~500 ms when using Push-to-Talk framework after beginTransmission
I’m working with the Push-to-Talk (PTT) framework and observing a consistent delay when starting audio capture. Scenario: A PTT call is already active The AVAudioSession is fully configured I request beginTransmission on the PTT channel I start my Audio Unit for recording (AudioOutputUnitStart) Observed behavior: AudioOutputUnitStart takes ~500 ms This happens whether I start the Audio Unit: after didBeginTransmission, or after AVAudioSession didActivate Comparison: Using the same Audio Unit, same format, and same configuration Without the PTT framework, AudioOutputUnitStart takes ~200 ms Additional notes: I am not modifying or reconfiguring AVAudioSession when requesting beginTransmission The audio session is already set up when the PTT call starts There are no interruptions or route changes at the time of starting the Audio Unit Impact: This extra latency is significant for Push-to-Talk use cases where fast transmit start is critical.
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330
Feb ’26
When to set AVAudioSession's preferredInput?
I want the audio session to always use the built-in microphone. However, when using the setPreferredInput() method like in this example private func enableBuiltInMic() { // Get the shared audio session. let session = AVAudioSession.sharedInstance() // Find the built-in microphone input. guard let availableInputs = session.availableInputs, let builtInMicInput = availableInputs.first(where: { $0.portType == .builtInMic }) else { print("The device must have a built-in microphone.") return } // Make the built-in microphone input the preferred input. do { try session.setPreferredInput(builtInMicInput) } catch { print("Unable to set the built-in mic as the preferred input.") } } and calling that function once in the initializer, the audio session still switches to the external microphone once one is plugged in. The session's preferredInput is nil again at that point, even if the built-in microphone is still listed in availableInputs. So, why is the preferredInput suddenly reset? when would be the appropriate time to set the preferredInput again? Observing the session’s availableInputs did not work and setting the preferredInput again in the routeChangeNotification handler seems a bad choice as it’s already a bit too late then.
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876
Oct ’25
Improving Speech Analyzer Transcription for technical terms
I am developing an app with transcription and I am exploring ways to improve the transcription from the SpeechAnalyzer/Transcriber for technical terms. SFSpeech... recognition had the capability of being augmented by contextualStrings. Does something similar exist for SpeechAnalyzer/Transcriber? If so please point me towards the documentation and any sample code that may exist for this. If there are other options, please let me know.
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298
Sep ’25
Crash while presenting a media picker for Music
This is the code I use: @MainActor func picker()->UIViewController{ let pickerController = MPMediaPickerController(mediaTypes: .music) print(pickerController) pickerController.showsCloudItems=true pickerController.prompt = NSLocalizedString("Add pieces to queue", comment:""); pickerController.allowsPickingMultipleItems=true; pickerController.delegate=MPMusicPlayerControllerSingleton.sharedController(); return pickerController } MainActor @IBAction func handleBrowserTapped(_ sender: AnyObject){ if let pickerController=contentProvider?.picker(){ self.present(pickerController, animated:true, completion:nil) } } And this his is the crash log: *** Assertion failure in -[MPMediaPickerController_Appex requestRemoteViewController], MPMediaPickerController.m:523 *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'remoteViewController cannot be nil -- process will crash inserting in hierarchy. We likely got a nil remoteViewController because Music is crashing.' *** First throw call stack: (0x1869cac70 0x183499224 0x1844f9f50 0x1a6c6a060 0x18d45518c 0x18d4cd410 0x103354544 0x10336dccc 0x10338f748 0x103364204 0x103364144 0x186957a64 0x1868e5288 0x1868e41d0 0x22bde7498 0x18c5a5ca0 0x18c510254 0x18c71ce90 0x103854340 0x1038542b0 0x103854430 0x1834f1c1c) libc++abi: terminating due to uncaught exception of type NSException *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'remoteViewController cannot be nil -- process will crash inserting in hierarchy. We likely got a nil remoteViewController because Music is crashing.'
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119
1d
AVAudioSession.outputVolume does not reflect system volume changes made while app is in background
I have a question regarding the behavior of AVAudioSession.sharedInstance().outputVolume. Observed behavior: When the app is in the foreground, I read audioSession.outputVolume (for example, 0.1). The app is then moved to the background. While the app is in the background, the user changes the system volume using the hardware buttons (for example, to 0.5). When the app returns to the foreground, audioSession.outputVolume still reports the previous value (0.1). From my testing, outputVolume only seems to update when the system volume is changed while the app is in the foreground. Volume changes made while the app is in the background are not reflected when the app returns to the foreground. Questions: According to Apple’s documentation for AVAudioSession.outputVolume: “The systemwide output volume set by the user.” https://developer.apple.com/documentation/avfaudio/avaudiosession/outputvolume However, based on our testing on iOS 18.6.2 and iOS 18.1, the observed behavior seems to differ from this description. Questions: The documentation states that outputVolume represents the system-wide volume set by the user. In our testing, the value does not reflect volume changes made while the app is in the background and only updates when the app is in the foreground.Is this the expected behavior of AVAudioSession.outputVolume? Is there any other recommended way in Swift to retrieve the current system volume that reflects user changes made both while the app is in the foreground and while it is in the background? Any clarification on the intended behavior or recommended handling would be greatly appreciated.
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191
3w
SpeechAnalyzer > AnalysisContext lack of documentation
I'm using the new SpeechAnalyzer framework to detect certain commands and want to improve accuracy by giving context. Seems like AnalysisContext is the solution for this, but couldn't find any usage example. So I want to make sure that I'm doing it right or not. let context = AnalysisContext() context.contextualStrings = [ AnalysisContext.ContextualStringsTag("commands"): [ "set speed level", "set jump level", "increase speed", "decrease speed", ... ], AnalysisContext.ContextualStringsTag("vocabulary"): [ "speed", "jump", ... ] ] try await analyzer.setContext(context) With this implementation, it still gives outputs like "Set some speed level", "It's speed level", etc. Also, is it possible to make it expect number after those commands, in order to eliminate results like "set some speed level to" (instead of two).
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490
Jan ’26
AirPods with H2 and studio-quality recording - how to replicate Camera video capture
Using an iPhone Pro 12 running iOS 26.0.1, with AirPods Pro 3. Camera app does capture video with what seems to be "Studio Quality Recording". Am trying to replicate that SQR with my own Camera like app, and while I can pull audio in from the APP3 mic, and my video capture app is recording a 48,000Hz high-bitrate video, the audio still sounds non-SQR. I'm seeing bluetoothA2DP , bluetoothLE , bluetoothHFP as portType, and not sure if SQR depends on one of those? Is there sample code demonstrating a SQR capture? Nevermind video and camera, just audio even? Also, I don't understand what SQR is doing between the APP3 and the iPhone. What codec is that? What bitrate is that? If I capture video using Capture and inspect the audio stream I see mono 74.14 kbit/s MPEG-4 AAC, 48000 Hz. But I assume that's been recompressed and not really giving me any insight into the APP3 H2 transmission?
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165
Oct ’25
How to safely switch between mic configurations on iOS?
I have an iPadOS M-processor application with two different running configurations. In config1, the shared AVAudioSession is configured for .videoChat mode using the built-in microphone. The input/output nodes of the AVAudioEngine are configured with voice processing enabled. The built-in mic is formatted for 1 channel at 48KHz. In config2, the shared AVAudioSession is configured for .measurement mode using an external USB microphone. The input/output nodes of the AVAudioEngine are configured with voice processing disabled. The external mic is formatted for 2 channels at 44.1KHz I've written a configuration manager designed to safely switch between these two configurations. It works by stopping AVAudioEngine and detaching all but the input and output nodes, updating the shared audio session for the desired mic and sample-rates, and setting the appropriate state for voice processing to either true or false as required by the configuration. Finally the new audio graph is constructed by attaching appropriate nodes, connecting them, and re-starting AVAudioEngine I'm experiencing what I believe is a race-condition between switching voice processing on or off and then trying to re-build and start the new audio graph. Even though notifications, which are dumped to the console indicate that my requested input and sample-rate settings are in place, I crash when trying to start the audio engine because the sample-rate is wrong. Investigating further it looks like the switch from remote I/O to voice-processing I/O or vice-versa has not yet actually completed. I introduced a 100ms second delay and that seems to help but is obviously not a reliable way to build software that must work consistently. How can I make sure that what are apparently asynchronous configuration changes to the shared audio session and the input/output nodes have completed before I go on? I tried using route change notifications from the shared AVAudioSession but these lie. They say my preferred mic input and sample-rate setting is in place but when I dump the AVAudioEngine graph to the debugger console, I still see the wrong sample rate assigned to the input/output nodes. Also these are the wrong AU nodes. That is, VPIO is still in place when RIO should be, or vice-versa. How can I make the switch reliable without arbitrary time delays? Is my configuration manager approach appropriate (question for Apple engineers)?
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275
Nov ’25
ShazamKit Background Operation Broken on iOS 18 - SHManagedSession Stops Working After ~20 Seconds
Your draft looks great! Here's a refined version with the iOS 17 comparison emphasized and slightly better flow: Hi Apple Engineers and fellow developers, I'm experiencing a critical regression with ShazamKit's background operation on iOS 18. ShazamKit's SHManagedSession stops identifying songs in the background after approximately 20 seconds on iOS 18, while the exact same code works perfectly on iOS 17. The behavior is consistent: the app works perfectly in the foreground, but when backgrounded or device is locked, it initially works for about 20 seconds then stops identifying new songs. The microphone indicator remains active suggesting audio access is maintained, but ShazamKit doesn't send identified songs in the background until you open the app again. Detection immediately resumes when bringing the app to foreground. My technical setup uses SHManagedSession for continuous matching with background modes properly configured in Info.plist including audio mode, and Background App Refresh enabled. I've tested this on physical devices running iOS 18.0 through 18.5 with the same results across all versions. The exact same code running on iOS 17 devices works flawlessly in the background. To reproduce: initialize SHManagedSession and start matching, begin song identification in foreground, background the app or lock device, play different songs which are initially detected for about 20 seconds, then after the timeout period new songs are no longer identified until you bring the app to foreground. This regression has impacted my production app as users who rely on continuous background music identification are experiencing a broken feature. I submitted this as Feedback ID FB15255903 last September with no solution so far. I've created a minimal demo project that reproduces this issue: https://github.com/tfmart/ShazamKitBackground Has anyone else experienced this ShazamKit background regression on iOS 18? Are there any known workarounds or alternative approaches? Given the time this issue has persisted, could we please get acknowledgment of this regression, expected timeline for a fix, or any recommended workarounds? Testing environment is Xcode 16.0+ on iOS 18.0-18.5 across multiple physical device models. Any guidance would be greatly appreciated.
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388
Jan ’26
Essentials of macOS to read and write mp3 and mp4 audio files
Hi, On macOS I used to open MP3 and MP4 files with ExtAudioFile. For a few years it doesn't work anymore. So I decided to try different macOS API using the AudioFileID of AudioToolbox framework. I decided to write a test: https://gist.github.com/joelkraehemann/7f5b241b52ca38c3a765c138fb647588 It fails right here: AudioFileOpenWithCallbacks() By telling OSStatus error 1954115647, which means kAudioFileUnsupportedFileTypeError. The filename was set to an MP4 file: ~/Music/test.mp4 Howto fix this? regards, Joël
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371
Jun ’25
How to get PID from AudioObjectID on macOS pre Sonoma
3 I am working on an application to get when input audio device is being used. Basically I want to know the application using the microphone (built-in or external) This app runs on macOS. For Mac versions starting from Sonoma I can use this code: int getAudioProcessPID(AudioObjectID process) { pid_t pid; if (@available(macOS 14.0, *)) { constexpr AudioObjectPropertyAddress prop { kAudioProcessPropertyPID, kAudioObjectPropertyScopeGlobal, kAudioObjectPropertyElementMain }; UInt32 dataSize = sizeof(pid); OSStatus error = AudioObjectGetPropertyData(process, &prop, 0, nullptr, &dataSize, &pid); if (error != noErr) { return -1; } } else { // Pre sonoma code goes here } return pid; } which works. However, kAudioProcessPropertyPID was added in macOS SDK 14.0. Does anyone know how to achieve the same functionality on previous versions?
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357
Sep ’25
MusicKit + AirPlay
Hello, I'm working on a MusicKit based SwiftUI app. I've integrated AirPlay using the AVRoutePickerView like so: struct UIKitAirPlayPickerView: UIViewRepresentable { func makeUIView(context: Context) -> AVRoutePickerView { let routePickerView = AVRoutePickerView() routePickerView.prioritizesVideoDevices = false return routePickerView } func updateUIView(_ uiView: AVRoutePickerView, context: Context) {} } The AirPlay menu appears as expected, and selecting an AirPlay device functions as expected. I'm currently sending audio from my app to a HomePod. However, the state of the AVRoutePickerView does not reflect the playback state. There is no cover art and it says "Not Playing". When my device is locked, my lock screen shows the album art, metadata and AirPlay routing as expected. My app uses the ApplicationMusicPlayer however I encounter the same behavior using the SystemMusicPlayer. Any guidance on how to troubleshoot this? Is there any other way to integrate the system AirPlay picker into my app, or is this my only option? Thank you for reading.
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325
3w
iOS - record audio fails to record
Hi, I try to record audio on the iPhone with the AVAudioRecorder and Xcode 26.0.1. Maybe the problem is that I can not record audio with the simulator. But there's a menu for audio. In the plist I added 'Privacy - Microphone Usage Description' and I ask for permission before recording. if await AVAudioApplication.requestRecordPermission() { print("permission granted") recordPermission = true } else { print("permission denied") } Permission is granted. let settings: [String : Any] = [ AVFormatIDKey: kAudioFormatMPEG4AAC, AVSampleRateKey: 12000, AVNumberOfChannelsKey: 1, AVEncoderAudioQualityKey: AVAudioQuality.high.rawValue ] recorder = try AVAudioRecorder(url: filename, settings: settings) let prepared = recorder.prepareToRecord() print("prepared started: \(prepared)") let started = recorder.record() print("recording started: \(started)") started is always false and I tried many settings. Error messages AddInstanceForFactory: No factory registered for id <CFUUID 0x600000211480> F8BB1C28-BAE8-11D6-9C31-00039315CD46 AudioConverter.cpp:1052 Failed to create a new in process converter -> from 0 ch, 12000 Hz, .... (0x00000000) 0 bits/channel, 0 bytes/packet, 0 frames/packet, 0 bytes/frame to 1 ch, 12000 Hz, aac (0x00000000) 0 bits/channel, 0 bytes/packet, 1024 frames/packet, 0 bytes/frame, with status -50 AudioQueueObject.cpp:1892 BuildConverter: AudioConverterNew returned -50 from: 0 ch, 12000 Hz, .... (0x00000000) 0 bits/channel, 0 bytes/packet, 0 frames/packet, 0 bytes/frame to: 1 ch, 12000 Hz, aac (0x00000000) 0 bits/channel, 0 bytes/packet, 1024 frames/packet, 0 bytes/frame prepared started: true AudioQueueObject.cpp:7581 ConvertInput: aq@0x10381be00: AudioConverterFillComplexBuffer returned -50, packetCount 5 recording started: false All examples I find are the same, but apparently there must be something different.
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340
Oct ’25