AVFoundation Video & Media-Engine Reference

API reference for AVFoundation's video write / export / render engine — the companion to the audio-focused AVFoundation reference. Covers the async writing and export APIs, the genuinely new iOS 27 capabilities, and the Swift-only deprecations that retire the old callback/KVO surface.

When to Use This Reference

Use this reference when:

• Writing or exporting video with AVAssetWriter or AVAssetExportSession
• Migrating off the Swift-deprecated export/write callbacks (exportAsynchronously, startWriting, progress, cancelExport)
• Adopting the concurrency-native sample-buffer Receiver pipeline
• Adding iOS 27 resumable export or segment-based writing
• Capturing in Apple Log / Apple Log 2, or detaching playback from system audio
• Driving simulator/device state from CI (see also the Device Hub workflow in axiom-build)

Example Prompts

Questions you can ask Claude that draw from this reference:

• "How do I migrate off exportAsynchronously in Swift 6?"
• "What replaces AVAssetWriter.startWriting() in iOS 27?"
• "How does resumable export work with configureForResumableExport?"
• "Show me the segment-based writing flow with AVAssetWritingPlanner."
• "How do I enqueue sample buffers with backpressure on the new Receiver?"
• "How do I record in Apple Log 2?"

What's Covered

Writing & export engine (iOS 26 baseline)

These predate iOS 27 — they're the targets of the iOS 27 Swift deprecations, and they work on an iOS 26 (or older) deployment floor, so migrating to them needs no availability gate.

• AVAssetWriter.start(), inputReceiver(for:), AVAssetWriterInput.SampleBufferReceiver
• AVAssetExportSession.export(to:as:) (async), states(updateInterval:) (AsyncSequence)

iOS 27 additions

• Resumable export – AVAssetExportSession.configureForResumableExport(), AVAssetExportSessionResumptionState
• Segment-based writing – AVAssetWritingPlanner (init(directoryForTemporaryFiles:), plan(_:segmentHandler:), executePlan()), AVAssetVideoTrackPlan
• Concurrency-native rendering – AVSampleBufferVideoRenderer.Receiver (and audio mirror): sampleBufferReceiver(adding:) on AVSampleBufferRenderSynchronizer, enqueue(_:) → EnqueueResult, renderingEventsAfterFinishedEnqueuing
• Apple Log 2 – AVVideoLogTransferFunctionKey, AVVideoLogTransferFunction_AppleLog / _AppleLog2
• Detach playback from system audio – AVPlayer.setDisconnectedFromSystemAudio(_:) (iOS/tvOS/watchOS/visionOS 27, not macOS)

Swift-only deprecations → migration

The old callback/KVO surface is deprecated in Swift only (ObjC unaffected): exportAsynchronously (iOS 18), progress / cancelExport / startWriting / per-input append (iOS 27) — each with its async replacement.

Concurrency posture

The media engine is async- and Sendable-first without broad @MainActor isolation; the async append/enqueue entry points are nonisolated(nonsending).

Documentation Scope

This page documents the avfoundation-video-ref skill. It is a reference skill — a comprehensive API guide without mandatory workflows.

• For AVFoundation audio (AVAudioSession, AVAudioEngine, spatial audio), see AVFoundation
• For the unified devicectl device/simulator inventory and the Device Hub workflow, see axiom-build
• For Swift 6 async/Sendable patterns underlying these APIs, see Swift Concurrency

Related Resources

• AVFoundation (audio) – audio session, engine, spatial audio
• Camera Capture – AVCaptureSession and recording
• WWDC 2026/256 – AVFoundation updates