🎬 VideoEditor (R&D Project)

VideoEditor is an R&D / educational iOS video editing app experiment targeting iOS 16.0+. The goal is to explore modern Swift, UIKit, and media technologies (e.g. AVFoundation) with a sustainable and testable architecture.

Production notice: This project is currently a “playground” and should not be considered production-ready.

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Project vision

• Modularity: Clear separation of UI, Domain, and Data layers.
• Testability: Dependencies are injected via DI.
• Simplicity: KISS principle; avoid unnecessary abstraction.
• UIKit-first: Screens are built with programmatic UIKit + Auto Layout.

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Requirements

• Xcode: 26.3
• iOS Deployment Target: 16.0+
• Language: Swift 5.5+

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Preview engine: from EditingProject to playback

The editor preview is not a raw file player. It rebuilds an AVFoundation composition from the current project state whenever you load or press play.

Pipeline overview

This diagram shows how EditorPlaybackManager coordinates loadPreview / play, how PreviewTimelineCompositionBuilder scans tracks and aggregates sources, and how the assembler + AVFoundation produce an AVPlayerItem for the preview layer.

Domain contract

• EditingProject (Domain/Models/): The serializable project — tracks, clips, timeline/source time ranges, export settings. Track order implies z-order (later tracks draw on top).
• CompositionBuilding (Domain/Protocols/CompositionBuilding.swift): build(from: EditingProject) → CompositionBuildResult (AVPlayerItem + AVComposition + AVVideoComposition, plus optional overlay layers).

Default engine (Engine/)

PreviewTimelineCompositionBuilder implements CompositionBuilding:

1. Computes project duration and a fixed preview render size (1080×1920).
2. Walks video and overlay tracks and turns each supported clip into internal preview sources (file video maps source range → timeline; still images use a tiny bundled donor video so AVFoundation has real samples).
3. PreviewCompositionAssembler (PreviewVideoCompositionCore.swift) builds an AVMutableComposition and a custom AVMutableVideoComposition (Core Image–based compositing for stacking, effects, transitions).
4. Audio clips are inserted on separate composition audio tracks; tracks are padded to the full project length with empty ranges where needed.
5. Wraps the composition in AVPlayerItem, attaches videoComposition / audioMix when present, and returns the result.

Other asset types (e.g. some identifiers) may be skipped until implemented — the builder only includes what it can turn into composition segments.

UI wiring (EditorPlaybackManager + editor screen)

• EditorViewModel.projectSnapshot() produces an EditingProject that reflects the current timeline (including edits). Playback always uses this snapshot, not a stale copy.
• EditorPlaybackManager holds a CompositionBuilding instance (default: PreviewTimelineCompositionBuilder), an AVPlayer, and an AVPlayerLayer placed inside EditorRenderView’s canvas.
• First appearance: EditorViewController calls loadPreview: build composition, attach/replace the player item, pause at time zero (thumbnail-style first frame).
• Toolbar play: play runs build again with the latest snapshot, then player.play(). Pause only pauses — no rebuild.

Playhead updates come from a periodic time observer on the player; reaching the end triggers pause and resets the toolbar play state.

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Roadmap

• Media import (Photos / Videos / Audio) ✅
• Timeline + trim media items ✅
• Create Composition builder (accepts image & video & audio and converts them into composition & playerItem) ✅
• Composition builder optimizations (working on it)
• EditorTimelineView optimizations for play, fast scrub debounce etc.
• Add transition between media items ✅
• Add overlay media items support like sticker and text
• Add applying effects to media items (like glitch etc)
• Add applying core image & custom filter to media items
• HDR support
• Higher render size support
• Export pipeline (presets/bitrate)