AVFoundation Audio Reference

API reference for AVFoundation audio — AVAudioSession, AVAudioEngine, bit-perfect USB DAC output, iOS 26+ spatial audio, and the iOS 27 async session and throwing engine APIs. It's for developers building playback, recording, or audio-processing features who need exact API names and platform availability.

When to Use This Reference

Use this reference when:

• Configuring audio session categories, modes, and options
• Handling interruptions and route changes, or moving to the iOS 27 deactivation and resumption notifications
• Building AVAudioEngine processing pipelines, taps, and format conversion
• Fixing iOS 27 deprecation warnings on connect, play(), or installTap
• Implementing USB DAC bit-perfect output
• Adding iOS 26+ input selection UI or AirPods high-quality recording
• Recording spatial audio or controlling Audio Mix

Example Prompts

Questions you can ask your assistant that will draw from this reference:

• "Which audio session category should a podcast player use?"
• "How do I activate my audio session without blocking the main thread on iOS 27?"
• "My interruption handler warns that InterruptionType is deprecated — what replaces it?"
• "How do I tell whether the system or my app deactivated the audio session?"
• "AVAudioEngine.connect is deprecated in iOS 27 — what do I use instead?"
• "How do I read samples from the read-only buffer that installAudioTap delivers?"
• "Can I write a realtime-safe AVAudioSourceNode render block in Swift?"
• "How do I let users pick a microphone with AVInputPickerInteraction?"
• "How do I record spatial audio with First Order Ambisonics?"

What's Covered

AVAudioSession

• Categories (.ambient, .soloAmbient, .playback, .record, .playAndRecord, .multiRoute)
• Modes (.default, .voiceChat, .videoChat, .gameChat, .videoRecording, .measurement, .moviePlayback, .spokenAudio)
• Options (.mixWithOthers, .duckOthers, .interruptSpokenAudioAndMixWithOthers, .allowBluetoothHFP, .allowBluetoothA2DP, .bluetoothHighQualityRecording, .defaultToSpeaker, .allowAirPlay)
• Interruption and route-change handling

Async activation and deactivation (iOS 27, not macOS)

• activate(options:), deactivate(options:), AVAudioSessionDeactivationOptions.notifyOthersOnDeactivation
• didBecomeActiveNotification, didBecomeInactiveNotification, resumptionRecommendationNotification
• DeactivationContext, InterruptionContext, ResumptionContext
• Typed messages — DidBecomeInactiveMessage (DeactivationResult), ResumptionRecommendationMessage
• Deprecated InterruptionType / InterruptionOptions
• AVAudioSession.Port.mediaDeviceExtension (iOS only)

AVAudioEngine

• Node types, connections, and pipelines
• Input taps and format conversion (AVAudioConverter)

Throwing engine and node APIs (iOS 27)

• connectNode(_:to:format:) and bus/connection-point variants, playAudio(), playAudio(at:)
• installAudioTap(onBus:bufferSize:format:tapProvider:), AVReadOnlyAudioPCMBuffer, channelData(_:)
• New AVAudioPCMBuffer accessors: channelData(_:), mutableChannelData(_:), init(copying:), withUnsafeAudioBufferList(_:)
• connectMIDI(_:to:format:eventListProvider:), AVMIDIEventListBlock
• AVAudioFormat.init(formatDescription:)
• Realtime-safe render and receiver blocks (Objective-C and C only)
• AVAudioUnitReverbPreset.outdoorGeneral

Bit-perfect output (USB DAC)

• Hardware-rate rendering, asking for the source rate with setPreferredSampleRate(_:), USB DAC routing

iOS 26+ features

• AVInputPickerInteraction
• AirPods high-quality recording
• Spatial audio capture (First Order Ambisonics), ASAF, APAC
• Audio Mix with the Cinematic framework (CNAssetSpatialAudioInfo, AUAudioMix)

Common patterns and anti-patterns

• Background audio playback, ducking other audio, Bluetooth device handling
• Wrong category, missing interruption handling, tap memory leaks, format mismatch crashes, forgetting to activate the session

Documentation Scope

This page documents the avfoundation-ref skill (in the axiom-media suite), an API reference with no mandatory workflow. The skill holds the code examples and anti-patterns your assistant uses when answering.

Related

• AVFoundation Video – The video write/export/render counterpart to this audio reference
• Camera Capture – AVCaptureSession setup, which also configures the audio session for spatial and AirPods recording
• Now Playing – Lock Screen and Control Center metadata for background audio playback
• Screen Capture – ScreenCaptureKit recording, which delivers app audio and microphone sample buffers alongside the screen

Resources

WWDC: 2025-251, 2025-403, 2019-510

Docs: /avfoundation, /avfaudio/avaudiosession, /avfaudio/avaudioengine, /avkit, /cinematic