LosslessCut (MP4)

LosslessCut (MP4) is a high-performance, open-source Android application for instant, lossless media trimming and merging. By manipulating compatible codecs (H.264, H.265, AAC) directly, it preserves original quality and processes files at lightning speed, remuxing them into standard .mp4 and .m4a containers without re-encoding.

✨ Features

• 🚀 Zero Quality Loss: Trims and merges video (.mp4) and audio (.m4a) using native MediaExtractor and MediaMuxer—no transcoding involved.
• 🎞️ Pro Timeline: Desktop-class NLE timeline supporting multi-segment editing (Split, Discard, and Drag).
• 🔍 Precision Seeking: Zoom up to 20x for frame-accurate edits.
• 🧲 Keyframe Snapping: Mandatory, strict keyframe snapping in lossless mode ensures frame-perfect cuts. Features haptic feedback and visual snapping.
• 📱 Adaptive UI: Ergonomic landscape sidebars and a unified floating player overlay for maximum screen real estate.
• ➕ Smart Playlist: Inline "Add Media" shortcut and intelligent duplicate detection on import.
• 🎵 Audio-Only Mode: Intelligent UI adaptation for audio files with waveform visualization.
• 📦 Batch Export & Merge: Export multiple "KEEP" regions as individual clips or merge them into a single seamless file in one pass.
• 🎼 Smart Audio Extraction: Automatically saves audio-only exports (when video is unchecked) as lossless .m4a files in the Music folder.
• ♿ Accessibility First: Comprehensive screen reader support via virtual view hierarchies (ExploreByTouchHelper).
• 🔄 Non-Destructive Workflow: Full Undo/Redo stack for all segment operations.
• 🤖 Smart Cut (v2.0): Unified, tabbed interface combining Silence Cut and Visual Detection.
  • Silence: Automated, parameterized removal of quiet sections with interactive "Ghost State" visualizations and live savings previews.
  • Visual: Algorithm-driven segment detection for Scene Changes, Black Frames, Freeze Frames, and Blur Quality.
• ⏸️ Intelligent Focus: Auto-pause playback when opening settings, export options, or silence detection to prevent missing content.
• ✨ Contextual UX: Seamless, auto-dismissing timeline hints and haptic feedback for a clean, professional interface.
• 💾 Project Persistence: Seamless session restoration—resume your edits exactly where you left off.
• 📂 Custom Output Path: Flexible export folder selection via Storage Access Framework (SAF).
• 🔄 Remux & Convert: Change container formats (e.g., MKV to MP4) instantly without re-encoding.
• 🏷️ Quick Metadata Fix: Correct video orientation and rotation flags in seconds.
• 🏗️ Clean Architecture: Context-free ViewModels and a centralized Repository pattern for maximum maintainability.
• 🧊 Format Compatibility: Optimized for modern codecs and containers (MP4, AAC). See Technical Reference for details.

📸 Screenshots

🛠️ How it Works

Unlike traditional video editors that decode and re-encode every frame, LosslessCut operates at the container level:

1. Probe: Scans the file structure to identify stream metadata and track availability.
2. Visualize: Renders a zoomable timeline where keyframes are marked as snapping points.
3. Mux: During export, the app extracts the original encoded samples between cut points and remuxes them into a new container. If the video track is excluded, it smartly routes to an audio-only .m4a container to preserve original quality.

🚀 Getting Started

Prerequisites

• Android Studio Koala+
• Android SDK 36 (Target) / 26 (Min)

Development

# Clone the repo
git clone https://github.com/tazztone/lossless-video-cut.git

# Generate icons (Consolidated tool)
java dev-scripts/asset-generate-icons.java

# Build debug APK using Gradle Kotlin DSL
./gradlew assembleDebug

🤝 Contributing

We follow MVVM + Clean Architecture with a strict separation between UI, Domain, and Data layers.

• Multi-Module: Core logic belongs in :core:domain, :core:data, or :engine.
• Use Cases: All business logic MUST reside in Use Cases within the :core:domain module.
• Workflow: Create a feature branch for every change and ensure CI passes before opening a PR.
• Code Style: Follow standard Kotlin conventions and avoid "God Classes".

🛡️ Security Policy

Reporting a Vulnerability

If you discover a security vulnerability within LosslessCut, please do not open a public issue. Instead, report it privately to the maintainers. We aim to respond to all reports within 48 hours and provide a fix or mitigation plan as soon as possible.

🔒 Permissions & Privacy

• Privacy-First Model: Removed all unnecessary runtime permissions (Notifications, Media Access). The app relies on the Storage Access Framework (SAF) for user-initiated file selection.
• Scoped Storage: Uses MediaStore to save results to Movies/LosslessCut (video) or Music/LosslessCut (audio extraction).
• Privacy: 100% offline. No analytics, no tracking, no data collection.

🗺️ Roadmap

• Smart Cut (v2.0): Integrated advanced algorithm-driven visual detection (Scene, Black, Freeze, Blur) and unified it with Silence Cut.
• Task Orchestration (Shelved: Background orchestration not required for near-instant exports)
• Advanced Tags: Title, artist, and creation date editing.
• Architectural Enforcement: Implement Konsist testing to safeguard module boundaries in the CI pipeline.
• Domain Purification: Extracted standard JVM domain module for maximum portability and testability.
• Metadata Tuning: Quick rotation and orientation flag fixes.
• Remux Utility: Instant container switching.
• Activity Decomposition: Refactored major UI logic into specialized delegates.
• Modern Build: Full migration to Gradle Kotlin DSL and AGP 9.0.

🛠️ Technical Reference

1. System Architecture

LosslessCut follows MVVM architecture with a focus on reactive UI and native media processing.

Tech Stack

• Languages: Kotlin 1.9+, Gradle Kotlin DSL (.gradle.kts)
• Media Engine: MediaExtractor, MediaMuxer (Processing), Media3 (Playback UI in :app)
• Dependency Inversion: Clean boundaries via :core:domain interfaces (JSR-330)
• Dependency Injection: Hilt (in Android modules)
• Minimum SDK: 26 (Android 8.0)
• Target SDK: 36 (Android 15)
• Tooling: AGP 9.0 (Built-in Kotlin Support), JVM 17 Toolchain

2. Project Structure

The project is organized into a modular feature/layer-based structure:

• :app: Main Android application module.
  • ui: Fragments (EditorFragment, RemuxFragment, MetadataFragment) and Navigation. VideoEditingActivity is now a thin host.
  • viewmodel: Jetpack ViewModels. VideoEditingViewModel delegates complex logic to Use Cases.
  • :core:domain: Pure Kotlin/JVM library. Contains Use Cases and domain interfaces. Zero Android/Hilt dependencies.
• :engine: Core media processing library. Decoupled from storage and Media3 via domain interfaces.
• :core:data: Shared data module containing models (MediaClip, TrimSegment), persistence (AppPreferences), and implementations of domain interfaces (IMediaFinalizer).

3. Component Blueprint

UI & Navigation

• Jetpack Navigation: Orchestrates transitions between editing modes.
• Fragments:
  • EditorFragment: Full NLE editor.
  • RemuxFragment: Simplified remux-only mode.
  • MetadataFragment: Metadata editing and rotation override.
• CustomVideoSeeker: A high-performance custom View for the NLE timeline.
  • Logic: Handles multi-touch (zoom), drag gestures for playhead and segments, and edge-auto-panning.
  • Accessibility: Implements ExploreByTouchHelper to expose virtual nodes for playhead and segment handles. Supports standard accessibility actions.
  • UX Polish: Implements auto-dismissing hint animations (e.g., "pinch to zoom") that disappear upon the first interaction.
  • Visuals: Draws segment colors, keyframe ticks, and zoom levels directly on the canvas for performance.
  • Waveform Caching: Uses LruCache to store pre-rendered 2048px bitmap tiles, replacing per-frame draw lines to dramatically improve scrubbing performance.
• Layout System: Uses orientation-specific layouts (layout vs layout-land) to maintain ergonomics.
  • Playlist Sidebar: Synced with ExoPlayer via robust Clip ID-based targeting. Blue border follows the Clip UUID, making it position-invariant.
  • Overlays: Semi-transparent overlays for player controls ensure unified UX across both orientations. Auto-pauses playback whenever a dialog or overlay (Settings, Silence Cut, Export) is opened.

3a. User Interaction Layer

• Smart Cut Tabbed Overlay: Unified controller (SmartCutOverlayController) managing:
  • SilenceDetectionOverlayController: audio-based detection.
  • VisualDetectionOverlayController: New video-based detection engine in :engine.
• Keyboard Shortcuts: Managed by ShortcutHandler.
  • SPACE: Play/Pause.
  • I / O: Set In/Out markers.
  • S: Split segment at current playhead position.
  • LEFT / RIGHT: Seek to previous/next keyframe.
  • ALT + LEFT/RIGHT: Nudge playhead via PlayerManager.performNudge.
• Share Intent Flow: MainActivity filters for ACTION_SEND/ACTION_VIEW. URIs are passed to VideoEditingActivity for probing.
• Playback Speed: Range: 0.25x, 0.5x, 1.0x, 1.5x, 2.0x, 4.0x.

Data & Domain Logic

• LosslessEngine: Core muxing orchestration.
  • executeLosslessCut: Trims a single file. Bypasses video-specific orientation hints if no video track is present.
  • executeLosslessMerge: Concatenates multiple MediaClip objects or segments. Handles PTS shifting.
• VideoEditingViewModel: State machine for the editor. Context-Free.
  • Architecture: No dependency on android.content.Context. All context-dependent operations (I/O) are delegated to the Repository.
  • Events: Uses a VideoEditingEvent sealed class via Channel for reliable one-time UI actions (e.g., ShowToast, ExportComplete).
  • Undo/Redo Stack: In-memory history of List<MediaClip> snapshots with synchronized canRedo flow logic.
  • Detection Engine:
    • Silence: Orchestrates DetectionUtils.findSilence using absolute rawAmplitudes from extracted waveformData to prevent false amplification of quiet clips.
    • Visual: Leverages VisualSegmentDetectorImpl in :engine for high-performance frame analysis using pure Kotlin algorithms (pHash, SAD, Laplacian variance) without native external libraries. Optimized with sequential frame processing via MediaExtractor.advance() rather than seek-based sampling, and features realtime progress callbacks.

Utilities

• StorageUtils: Handles Scoped Storage. Centralizes URI creation, dynamically selecting Movies/LosslessCut or Music/LosslessCut based on media type.
• TimeUtils: Formatting and precision conversion between MS and microseconds.
• Permission Management: Relies primarily on the Storage Access Framework (SAF). Broad runtime permissions are avoided for enhanced privacy and UX.

4. Key Workflows

Lossless Export Process

1. MediaExtractor seeks to the nearest keyframe before the requested startMs.
2. Encoded samples are read and passed to MediaMuxer.
3. Samples before startMs are discarded by the muxer logic based on timestamp.
4. Samples are written until endMs.

Multi-Clip Merging

• Validates track compatibility (codecs must match for lossless concatenation).
• Shifts sample PTS values by the cumulative duration of previous segments to ensure continuity.

5. Development & CI

• Testing:
  • JVM: ./gradlew test (Robolectric).
  • Android: ./gradlew connectedAndroidTest (Espresso).
• Scripts: dev-scripts/ contains IconGenerator.java and maintenance scripts like project-clean.sh.
• CI/CD: GitHub Actions (release.yml) builds and signs production APKs on tag push. Includes a Lint gate and static analysis with Detekt.

6. Context7 Library IDs

Use these IDs for documentation queries:

• /androidx/media (Media3/ExoPlayer)
• /kotlin/kotlinx.coroutines (Concurrency)
• /androidx/datastore (Preferences)
• /material-components/material-components-android (UI)

7. Format Compatibility

LosslessCut is designed for maximum speed and compatibility by leveraging Android's native MediaMuxer for MP4/MPEG-4 output.

Category	Primary Support (Optimized)	Legacy/Technical Support
Output Container	.mp4, .m4a	—
Video Codecs	H.264 (AVC), H.265 (HEVC)	H.263, MPEG-4 Visual (ES)
Audio Codecs	AAC (LC, HE)	AMR-NB, AMR-WB
Input Container	.mp4, .m4a, .mov, .mkv*	.3gp, .webm*

* MKV/WebM inputs can be remuxed to MP4 ONLY if the internal codecs match the supported list above.

Important

Why are these the only supported formats? Standard Android APIs (MediaMuxer) enforce strict compliance for the MP4 container. Codecs like MP3, FLAC, VP9, or Vorbis require transcoding (re-encoding) to fit into an MP4 file, which would defeat the "lossless" purpose of this app.

Tip

Pro Tip: If your file is a .mov or .mkv with H.264/AAC, LosslessCut will handle it perfectly by remuxing the streams into a new .mp4 file.

📄 License

Licensed under the MIT License. See LICENSE for details.