axiom-camera-capture

name	axiom-camera-capture
description	AVCaptureSession, camera preview, photo capture, video recording, RotationCoordinator, session interruptions, deferred processing, capture responsiveness, zero-shutter-lag, photoQualityPrioritization, front camera mirroring
license	MIT
compatibility	iOS 17+, iPadOS 17+, macOS 14+, tvOS 17+, axiom-visionOS 1+
metadata	{"version":"1.0.0","last-updated":"2026-01-03"}

Camera Capture with AVFoundation

Guides you through implementing camera capture: session setup, photo capture, video recording, responsive capture UX, rotation handling, and session lifecycle management.

When to Use This Skill

Use when you need to:

• ☑ Build a custom camera UI (not system picker)
• ☑ Capture photos with quality/speed tradeoffs
• ☑ Record video with audio
• ☑ Handle device rotation correctly (RotationCoordinator)
• ☑ Make capture feel responsive (zero-shutter-lag)
• ☑ Handle session interruptions (phone calls, multitasking)
• ☑ Switch between front/back cameras
• ☑ Configure capture quality and resolution

Example Prompts

"How do I set up a camera preview in SwiftUI?" "My camera freezes when I get a phone call" "The photo preview is rotated wrong on front camera" "How do I make photo capture feel instant?" "Should I use deferred processing?" "My camera takes too long to capture" "How do I switch between front and back cameras?" "How do I record video with audio?"

Red Flags

Signs you're making this harder than it needs to be:

• ❌ Calling startRunning() on main thread (blocks UI for seconds)
• ❌ Using deprecated videoOrientation instead of RotationCoordinator (iOS 17+)
• ❌ Not observing session interruptions (app freezes on phone call)
• ❌ Creating new AVCaptureSession for each capture (expensive)
• ❌ Using .photo preset for video (wrong format)
• ❌ Ignoring photoQualityPrioritization (slow captures)
• ❌ Not handling .notAuthorized permission state
• ❌ Modifying session without beginConfiguration()/commitConfiguration()
• ❌ Using UIImagePickerController for custom camera UI (limited control)

Mandatory First Steps

Before implementing any camera feature:

1. Choose Your Capture Mode

What do you need?

┌─ Just let user pick a photo?
│  └─ Don't use AVFoundation - use PHPicker or PhotosPicker
│     See: /skill axiom-photo-library
│
├─ Simple photo/video capture with system UI?
│  └─ UIImagePickerController (but limited customization)
│
├─ Custom camera UI with photo capture?
│  └─ AVCaptureSession + AVCapturePhotoOutput
│     → Continue with this skill
│
├─ Custom camera UI with video recording?
│  └─ AVCaptureSession + AVCaptureMovieFileOutput
│     → Continue with this skill
│
└─ Both photo and video in same session?
   └─ AVCaptureSession + both outputs
      → Continue with this skill

2. Request Camera Permission

import AVFoundation

func requestCameraAccess() async -> Bool {
    let status = AVCaptureDevice.authorizationStatus(for: .video)

    switch status {
    case .authorized:
        return true
    case .notDetermined:
        return await AVCaptureDevice.requestAccess(for: .video)
    case .denied, .restricted:
        // Show settings prompt
        return false
    @unknown default:
        return false
    }
}

Info.plist required:

<key>NSCameraUsageDescription</key>
<string>Take photos and videos</string>

For audio (video recording):

<key>NSMicrophoneUsageDescription</key>
<string>Record audio with video</string>

3. Understand Session Architecture

AVCaptureSession
    ├─ Inputs
    │   ├─ AVCaptureDeviceInput (camera)
    │   └─ AVCaptureDeviceInput (microphone, for video)
    │
    ├─ Outputs
    │   ├─ AVCapturePhotoOutput (photos)
    │   ├─ AVCaptureMovieFileOutput (video files)
    │   └─ AVCaptureVideoDataOutput (raw frames)
    │
    └─ Connections (automatic between compatible input/output)

Key rule: All session configuration happens on a dedicated serial queue, never main thread.

Core Patterns

Pattern 1: Basic Session Setup

Use case: Set up camera preview with photo capture capability.

import AVFoundation

class CameraManager: NSObject {
    let session = AVCaptureSession()
    let photoOutput = AVCapturePhotoOutput()

    // CRITICAL: Dedicated serial queue for session work
    private let sessionQueue = DispatchQueue(label: "camera.session")

    func setupSession() {
        sessionQueue.async { [self] in
            session.beginConfiguration()
            defer { session.commitConfiguration() }

            // 1. Set session preset
            session.sessionPreset = .photo

            // 2. Add camera input
            guard let camera = AVCaptureDevice.default(.builtInWideAngleCamera,
                                                        for: .video,
                                                        position: .back),
                  let input = try? AVCaptureDeviceInput(device: camera),
                  session.canAddInput(input) else {
                return
            }
            session.addInput(input)

            // 3. Add photo output
            guard session.canAddOutput(photoOutput) else { return }
            session.addOutput(photoOutput)

            // 4. Configure photo output
            photoOutput.isHighResolutionCaptureEnabled = true
            photoOutput.maxPhotoQualityPrioritization  .quality
        }
    }

     () {
        sessionQueue.async { [] 
             session.isRunning {
                session.startRunning()  
            }
        }
    }

     () {
        sessionQueue.async { [] 
             session.isRunning {
                session.stopRunning()
            }
        }
    }
}

Cost: 30 min implementation

Pattern 2: SwiftUI Camera Preview

Use case: Display camera preview in SwiftUI view.

import SwiftUI
import AVFoundation

struct CameraPreview: UIViewRepresentable {
    let session: AVCaptureSession

    func makeUIView(context: Context) -> PreviewView {
        let view = PreviewView()
        view.previewLayer.session = session
        view.previewLayer.videoGravity = .resizeAspectFill
        return view
    }

    func updateUIView(_ uiView: PreviewView, context: Context) {}

    class PreviewView: UIView {
        override class var layerClass: AnyClass { AVCaptureVideoPreviewLayer.self }
        var previewLayer: AVCaptureVideoPreviewLayer { layer as! AVCaptureVideoPreviewLayer }
    }
}

// Usage in SwiftUI
struct CameraView: View {
    @StateObject private var camera = CameraManager()

    var body: some View {
        (session: camera.session)
            .ignoresSafeArea()
            .onAppear { camera.startSession() }
            .onDisappear { camera.stopSession() }
    }
}

Cost: 20 min implementation

Pattern 3: Rotation Handling with RotationCoordinator (iOS 17+)

Use case: Keep preview and captured photos correctly oriented regardless of device rotation.

Why RotationCoordinator: Deprecated videoOrientation requires manual observation of device orientation. RotationCoordinator automatically tracks gravity and provides angles.

import AVFoundation

class CameraManager {
    private var rotationCoordinator: AVCaptureDevice.RotationCoordinator?
    private var rotationObservation: NSKeyValueObservation?

    func setupRotationCoordinator(device: AVCaptureDevice, previewLayer: AVCaptureVideoPreviewLayer) {
        // Create coordinator with device and preview layer
        rotationCoordinator = AVCaptureDevice.RotationCoordinator(
            device: device,
            previewLayer: previewLayer
        )

        // Observe preview rotation changes
        rotationObservation = rotationCoordinator?.observe(
            \.videoRotationAngleForHorizonLevelPreview,
            options: [.new]
        ) { [weak previewLayer] coordinator, _ in
            // Update preview layer rotation on main thread
            DispatchQueue.main.async {
                previewLayer?.connection?.videoRotationAngle = coordinator.videoRotationAngleForHorizonLevelPreview
            }
        }

        // Set initial rotation
        previewLayer.connection?.videoRotationAngle = rotationCoordinator!.videoRotationAngleForHorizonLevelPreview
    }

    func captureRotationAngle() -> CGFloat {
        // Use this angle when capturing photos
        rotationCoordinator?.videoRotationAngleForHorizonLevelCapture  
    }
}

When capturing:

func capturePhoto() {
    let settings = AVCapturePhotoSettings()

    // Apply rotation angle from coordinator
    if let connection = photoOutput.connection(with: .video) {
        connection.videoRotationAngle = captureRotationAngle()
    }

    photoOutput.capturePhoto(with: settings, delegate: self)
}

Cost: 45 min implementation, prevents 2+ hours debugging rotation issues

Pattern 4: Responsive Capture Pipeline (iOS 17+)

Use case: Make photo capture feel instant with zero-shutter-lag, overlapping captures, and responsive button states.

iOS 17+ introduces four complementary APIs that work together for maximum responsiveness:

4a. Zero Shutter Lag

Uses a ring buffer of recent frames to "time travel" back to the exact moment you tapped the shutter. Enabled automatically for iOS 17+ apps.

// Check if supported for current format
if photoOutput.isZeroShutterLagSupported {
    // Enabled by default for apps linking iOS 17+
    // Opt out if causing issues:
    // photoOutput.isZeroShutterLagEnabled = false
}

Why it matters: Without ZSL, there's a delay between tap and frame capture. For action shots, the moment is already over.

Requirements: iPhone XS and newer. Does NOT apply to flash captures, manual exposure, bracketed captures, or constituent photo delivery.

4b. Responsive Capture (Overlapping Captures)

Allows a new capture to start while the previous one is still processing:

// Check support first
if photoOutput.isZeroShutterLagSupported {
    photoOutput.isZeroShutterLagEnabled = true  // Required for responsive capture

    if photoOutput.isResponsiveCaptureSupported {
        photoOutput.isResponsiveCaptureEnabled = true
    }
}

Tradeoff: Increases peak memory usage. If your app is memory-constrained, consider leaving disabled.

Requirements: A12 Bionic (iPhone XS) and newer.

4c. Fast Capture Prioritization

Automatically adapts quality when taking multiple photos rapidly (like burst mode):

if photoOutput.isFastCapturePrioritizationSupported {
    photoOutput.isFastCapturePrioritizationEnabled = true
    // When enabled, rapid captures use "balanced" quality instead of "quality"
    // to maintain consistent shot-to-shot time
}

When to enable: User-facing toggle ("Prioritize Faster Shooting" in Camera.app). Off by default because it reduces quality.

4d. Readiness Coordinator (Button State Management)

Critical for UX: Provides synchronous updates for shutter button state without async lag.

class CameraManager {
    private var readinessCoordinator: AVCapturePhotoOutputReadinessCoordinator!

    func setupReadinessCoordinator() {
        readinessCoordinator = AVCapturePhotoOutputReadinessCoordinator(photoOutput: photoOutput)
        readinessCoordinator.delegate = self
    }

    func capturePhoto() {
        var settings = AVCapturePhotoSettings()
        settings.photoQualityPrioritization = .balanced

        // Tell coordinator to track this capture BEFORE calling capturePhoto
        readinessCoordinator.startTrackingCaptureRequest(using: settings)

        photoOutput.capturePhoto(with: settings, delegate: self)
    }
}

extension CameraManager: AVCapturePhotoOutputReadinessCoordinatorDelegate {
    func readinessCoordinator(_ coordinator: AVCapturePhotoOutputReadinessCoordinator,
                              captureReadinessDidChange captureReadiness: AVCapturePhotoOutput.CaptureReadiness) {
        DispatchQueue.main.async {
            switch captureReadiness {
            case .ready:
                self.shutterButton.isEnabled = true
                self.shutterButton.alpha = 1.0

            case .notReadyMomentarily:
                
                .shutterButton.isEnabled  

             .notReadyWaitingForCapture:
                
                .shutterButton.alpha  

             .notReadyWaitingForProcessing:
                
                .showProcessingIndicator()

             .sessionNotRunning:
                .shutterButton.isEnabled  

             :
                
            }
        }
    }
}

Why use Readiness Coordinator: Without it, you'd need to track capture state manually and users might spam the shutter button during processing.

Quality Prioritization (Baseline)

Still useful even without the new APIs:

func capturePhoto() {
    var settings = AVCapturePhotoSettings()

    // Speed vs Quality tradeoff
    // .speed     - Fastest capture, lower quality
    // .balanced  - Good default
    // .quality   - Best quality, may have delay
    settings.photoQualityPrioritization = .speed

    // For specific use cases:
    // - Social sharing: .speed (users expect instant)
    // - Document scanning: .quality (accuracy matters)
    // - General photography: .balanced

    photoOutput.capturePhoto(with: settings, delegate: self)
}

Deferred Processing (iOS 17+):

For maximum responsiveness, capture returns immediately with proxy image, full Deep Fusion processing happens in background:

// Check support and enable deferred processing
if photoOutput.isAutoDeferredPhotoDeliverySupported {
    photoOutput.isAutoDeferredPhotoDeliveryEnabled = true
}

Delegate callbacks with deferred processing:

// Called for BOTH regular photos AND deferred proxies
func photoOutput(_ output: AVCapturePhotoOutput,
                 didFinishProcessingPhoto photo: AVCapturePhoto,
                 error: Error?) {
    guard error == nil else { return }

    // Non-deferred photo - save directly
    if !photo.isRawPhoto, let data = photo.fileDataRepresentation() {
        savePhotoToLibrary(data)
    }
}

// Called ONLY for deferred proxies - save to PhotoKit for later processing
func photoOutput(_ output: AVCapturePhotoOutput,
                 didFinishCapturingDeferredPhotoProxy deferredPhotoProxy: AVCaptureDeferredPhotoProxy,
                 error: Error?) {
    guard error == nil else { return }

    // CRITICAL: Save proxy to library ASAP before app is backgrounded
    // App may be force-quit if memory pressure is high during backgrounding
    guard let proxyData = deferredPhotoProxy.fileDataRepresentation() else { return }

    Task {
        try  .shared().performChanges {
             request  .forAsset()
            
            request.addResource(with: .photoProxy, data: proxyData, options: )
        }
    }
}

When final processing happens:

• On-demand when image is requested from PhotoKit
• Or automatically when device is idle (plugged in, not in use)

Fetching images with deferred processing awareness:

// Request with secondary degraded image for smoother UX
let options = PHImageRequestOptions()
options.allowSecondaryDegradedImage = true  // New in iOS 17

PHImageManager.default().requestImage(
    for: asset,
    targetSize: targetSize,
    contentMode: .aspectFill,
    options: options
) { image, info in
    let isDegraded = info?[PHImageResultIsDegradedKey] as? Bool ?? false

    if isDegraded {
        // First: Low quality (immediate)
        // Second: Medium quality (new - while processing)
        // Third callback will be final quality
        self.showTemporaryImage(image)
    } else {
        // Final quality - processing complete
        self.showFinalImage(image)
    }
}

Requirements: iPhone 11 Pro and newer. Not used for flash captures or formats that don't benefit from extended processing.

Important considerations:

• Can't apply pixel buffer customizations (filters, metadata changes) to deferred photos
• Use PhotoKit adjustments after processing for edits
• Get proxy into library ASAP - limited time when backgrounded

Cost: 1 hour implementation, prevents "camera feels slow" complaints

Pattern 5: Session Interruption Handling

Use case: Handle phone calls, multitasking, system camera usage.

class CameraManager {
    private var interruptionObservers: [NSObjectProtocol] = []

    func setupInterruptionHandling() {
        // Session was interrupted
        let interruptedObserver = NotificationCenter.default.addObserver(
            forName: .AVCaptureSessionWasInterrupted,
            object: session,
            queue: .main
        ) { [weak self] notification in
            guard let reason = notification.userInfo?[AVCaptureSessionInterruptionReasonKey] as? Int,
                  let interruptionReason = AVCaptureSession.InterruptionReason(rawValue: reason) else {
                return
            }

            switch interruptionReason {
            case .videoDeviceNotAvailableInBackground:
                // App went to background - normal, will resume
                self?.showPausedOverlay()

            case .audioDeviceInUseByAnotherClient:
                // Another app using audio
                self?.showInterruptedBanner("Audio in use by another app")

            case .videoDeviceInUseByAnotherClient:
                // Another app using camera
                self?.showInterruptedBanner()

             .videoDeviceNotAvailableWithMultipleForegroundApps:
                
                .showInterruptedBanner()

             .videoDeviceNotAvailableDueToSystemPressure:
                
                .handleThermalPressure()

             :
                .showInterruptedBanner()
            }
        }
        interruptionObservers.append(interruptedObserver)

        
         endedObserver  .default.addObserver(
            forName: .,
            object: session,
            queue: .main
        ) { [ ]  
            .hideInterruptedBanner()
            .hidePausedOverlay()
            
        }
        interruptionObservers.append(endedObserver)
    }

     {
        interruptionObservers.forEach { .default.removeObserver() }
    }
}

Cost: 30 min implementation, prevents "camera freezes" bug reports

Pattern 6: Camera Switching (Front/Back)

Use case: Toggle between front and back cameras.

func switchCamera() {
    sessionQueue.async { [self] in
        guard let currentInput = session.inputs.first as? AVCaptureDeviceInput else {
            return
        }

        let currentPosition = currentInput.device.position
        let newPosition: AVCaptureDevice.Position = currentPosition == .back ? .front : .back

        guard let newDevice = AVCaptureDevice.default(
            .builtInWideAngleCamera,
            for: .video,
            position: newPosition
        ) else {
            return
        }

        session.beginConfiguration()
        defer { session.commitConfiguration() }

        // Remove old input
        session.removeInput(currentInput)

        // Add new input
        do {
            let newInput = try AVCaptureDeviceInput(device: newDevice)
            if session.canAddInput(newInput) {
                session.addInput(newInput)

                // Update rotation coordinator for new device
                if let previewLayer = previewLayer {
                    setupRotationCoordinator(device: newDevice, previewLayer: previewLayer)
                }
            } else {
                // Fallback: restore old input
                session.addInput(currentInput)
            }
        }  {
            session.addInput(currentInput)
        }
    }
}

Front camera mirroring: Front camera preview is mirrored by default (matches user expectation). Captured photos are NOT mirrored (correct for sharing). This is intentional.

Cost: 20 min implementation

Pattern 7: Video Recording

Use case: Record video with audio to file.

class CameraManager: NSObject {
    let movieOutput = AVCaptureMovieFileOutput()
    private var currentRecordingURL: URL?

    func setupVideoRecording() {
        sessionQueue.async { [self] in
            session.beginConfiguration()
            defer { session.commitConfiguration() }

            // Set video preset
            session.sessionPreset = .high  // Or .hd1920x1080, .hd4K3840x2160

            // Add microphone input
            if let microphone = AVCaptureDevice.default(for: .audio),
               let audioInput = try? AVCaptureDeviceInput(device: microphone),
               session.canAddInput(audioInput) {
                session.addInput(audioInput)
            }

            // Add movie output
            if session.canAddOutput(movieOutput) {
                session.addOutput(movieOutput)
            }
        }
    }

    func startRecording() {
        guard !movieOutput.isRecording else { return }

        let outputURL = FileManager.default.temporaryDirectory
            .appendingPathComponent(UUID().uuidString)
            .appendingPathExtension("mov")

        currentRecordingURL = outputURL

        // Apply rotation
          connection  movieOutput.connection(with: .video) {
            connection.videoRotationAngle  captureRotationAngle()
        }

        movieOutput.startRecording(to: outputURL, recordingDelegate: )
    }

     () {
         movieOutput.isRecording  {  }
        movieOutput.stopRecording()
    }
}

 :  {
     ( : ,
                     : ,
                     : [],
                    : ?) {
          error  error {
            ()
            
        }

        
        saveVideoToPhotoLibrary(outputFileURL)
    }
}

Cost: 45 min implementation

Anti-Patterns

Anti-Pattern 1: Session Work on Main Thread

Wrong:

func startCamera() {
    session.startRunning()  // Blocks UI for 1-3 seconds!
}

Right:

func startCamera() {
    sessionQueue.async { [self] in
        session.startRunning()
    }
}

Why it matters: startRunning() is blocking. On main thread, UI freezes.

Anti-Pattern 2: Using Deprecated videoOrientation

Wrong (pre-iOS 17):

// Manually tracking orientation
NotificationCenter.default.addObserver(
    forName: UIDevice.orientationDidChangeNotification,
    object: nil,
    queue: .main
) { _ in
    // Manual rotation logic...
}

Right (iOS 17+):

let coordinator = AVCaptureDevice.RotationCoordinator(device: camera, previewLayer: preview)
// Automatically tracks gravity, provides angles

Why it matters: RotationCoordinator handles edge cases (face-up, face-down) that manual tracking misses.

Anti-Pattern 3: Ignoring Session Interruptions

Wrong:

// No interruption handling - camera freezes on phone call

Right:

NotificationCenter.default.addObserver(
    forName: .AVCaptureSessionWasInterrupted,
    object: session,
    queue: .main
) { notification in
    // Show UI feedback
}

Why it matters: Without handling, camera appears frozen when interrupted.

Anti-Pattern 4: Modifying Session Without Configuration Block

Wrong:

session.removeInput(oldInput)
session.addInput(newInput)  // May fail mid-stream

Right:

session.beginConfiguration()
session.removeInput(oldInput)
session.addInput(newInput)
session.commitConfiguration()  // Atomic change

Why it matters: Without configuration block, session may enter invalid state between calls.

Pressure Scenarios

Scenario 1: "Just Make the Camera Work by Friday"

Context: Product wants camera feature shipped. You're considering skipping interruption handling.

Pressure: "It works when I test it, let's ship."

Reality: First user who gets a phone call while using camera will see frozen UI. App Store review may catch this.

Correct action:

1. Implement interruption handling (30 min)
2. Test by calling your test device during camera use
3. Verify UI shows appropriate feedback

Push-back template: "Camera captures work, but the app freezes if a phone call comes in. I need 30 minutes to handle interruptions properly and avoid 1-star reviews."

Scenario 2: "The Camera is Too Slow"

Context: QA reports photo capture feels sluggish. PM wants it "instant like the system camera."

Pressure: "Just make it faster somehow."

Reality: Default settings prioritize quality over speed. System camera uses deferred processing.

Correct action:

1. Set photoQualityPrioritization = .speed for social/sharing use cases
2. Consider deferred processing for maximum responsiveness
3. Show capture animation immediately (before processing completes)

Push-back template: "We're currently optimizing for image quality. I can make capture feel instant by prioritizing speed and showing the preview immediately while processing continues in background. This is what the system Camera app does."

Scenario 3: "Why is the Front Camera Photo Mirrored?"

Context: Designer reports front camera photos look "wrong" - they're not mirrored like the preview.

Pressure: "The preview shows it one way, the photo should match."

Reality: Preview is mirrored (user expectation - like a mirror). Photo is NOT mirrored (correct for sharing - text reads correctly). This is intentional behavior matching system camera.

Correct action:

1. Explain this is Apple's standard behavior
2. If business requires mirrored photos (selfie apps), manually mirror in post-processing
3. Never mirror the preview differently than expected

Push-back template: "This is intentional Apple behavior. The preview is mirrored like a mirror so users can frame themselves, but the captured photo is unmirrored so text reads correctly when shared. We can add optional mirroring in post-processing if our use case requires it."

Checklist

Before shipping camera features:

Session Setup:

• ☑ All session work on dedicated serial queue
• ☑ startRunning() never called on main thread
• ☑ Session preset matches use case (.photo for photos, .high for video)
• ☑ Configuration changes wrapped in beginConfiguration()/commitConfiguration()

Permissions:

• ☑ Camera permission requested before session setup
• ☑ NSCameraUsageDescription in Info.plist
• ☑ NSMicrophoneUsageDescription if recording audio
• ☑ Graceful handling of denied permission

Rotation:

• ☑ RotationCoordinator used (not deprecated videoOrientation)
• ☑ Preview layer rotation updated via observation
• ☑ Capture rotation angle applied when taking photos
• ☑ Tested in all orientations (portrait, landscape, face-up)

Responsiveness:

• ☑ photoQualityPrioritization set appropriately for use case
• ☑ Capture button shows immediate feedback
• ☑ Deferred processing considered for maximum speed

Interruptions:

• ☑ Session interruption observer registered
• ☑ UI feedback shown when interrupted
• ☑ Tested with incoming phone call
• ☑ Tested in Split View (iPad)

Camera Switching:

• ☑ Front/back switch updates rotation coordinator
• ☑ Switch happens on session queue
• ☑ Fallback if new camera unavailable

Video Recording (if applicable):

• ☑ Microphone input added
• ☑ Recording delegate handles completion
• ☑ File cleanup for temporary recordings

Resources

WWDC: 2021-10247, 2023-10105

Docs: /avfoundation/avcapturesession, /avfoundation/avcapturedevice/rotationcoordinator, /avfoundation/avcapturephotosettings, /avfoundation/avcapturephotooutputreadinesscoordinator

Skills: axiom-camera-capture-ref, axiom-camera-capture-diag, axiom-photo-library