MP4Flow

A local, native macOS video-to-MP4 converter.

MP4Flow converts common video files to playable MP4 on your Mac. It replaces codec jargon with clear choices: keep the original, save space, use a compatible format, trim, crop, rotate, or merge clips. Nothing is uploaded.

Beyond MP4 conversion, use MP4Flow to trim clips, crop the frame, and rotate video. We are building a fast, lightweight, free, and open-source video conversion tool that feels at home on macOS.

Add a video, make quick edits, and convert it locally.

中文说明 · Installer guide · Media regression · Release checklist · Privacy · Security

Highlights

• English and Simplified Chinese UI — follows the system language on first launch and can be changed in the app.
• Fast when possible — direct MP4 remuxing and stream-copy trimming avoid re-encoding; supported H.264/HEVC scaling uses Apple VideoToolbox.
• Clear choices — Smart Convert, Clear and Compact, Preserve Original Quality, device-compatible H.264, smaller HEVC, and a software fallback.
• Resolution control — keep original dimensions or convert to 1080p, 720p, 576p, or 480p while preserving aspect ratio. Upscaling enlarges the canvas, not missing detail.
• Experimental Smart Enhance Upscale — on Apple Silicon running macOS 27 or later, use VideoToolbox super resolution for the exact scale factors reported by the system. It is intentionally opt-in, supports no crop or rotation yet, and may require a one-time system model download.
• Simple editing — trim a time range, crop with draggable handles and numeric fields, and rotate 90° or 180°.
• Two merge modes — lossless merging for matching streams; compatible merging normalises clips to the largest source resolution without stretching.
• Reliable batches — progress, retry failed items, cancellation, safe temporary outputs, and no overwrite of existing files.
• Privacy by design — processing stays on your Mac. Outputs are configured not to copy container metadata or chapters; review exports when sensitive redaction matters.

Requirements

• macOS 13 Ventura or later
• FFmpeg and ffprobe installed together in /opt/homebrew/bin, /usr/local/bin, /opt/local/bin, or /usr/bin
• Apple Silicon or Intel Mac; hardware acceleration depends on the Mac and source codec
• Smart Enhance Upscale (experimental): Apple Silicon, macOS 27 or later, and a source/target pair that matches a VideoToolbox-supported scale factor. The system may download its model before the first use. It is not bundled with MP4Flow and does not send your video to MP4Flow or a third-party service.

Install FFmpeg with Homebrew:

brew install ffmpeg

Use

1. Open MP4Flow and add video files or drag them into the queue.
2. Choose a conversion mode, quality/size, resolution, and output location.
3. Optionally use Trim, Crop, or Rotate on a waiting item.
4. Select Start Conversion. Completed files can be revealed in Finder.

To merge, add at least two untouched waiting files and select Merge. Choose Compatible Merge when their stream parameters differ.

Build from source

git clone https://github.com/ixiehao/MP4Flow.git
cd MP4Flow
./Scripts/build-app.sh
open MP4Flow.app

The generated app is ad-hoc signed for local development. See docs/INSTALLER-BUILD.md to create a distributable DMG.

Media regression

With FFmpeg installed, run the synthetic media suite before a release:

./Scripts/run-media-regression.sh

It creates and removes tiny project-owned fixtures for H.264, HEVC, VFR, portrait video, audio/subtitle variants, rotation, HDR signalling, unusual dimensions, long-duration scheduling, special file names, and corrupt input. See the media regression gate for its limits and the real-device matrix required for a public release.

Dependencies and licensing

• MP4Flow uses Swift, SwiftUI, and Apple system frameworks.
• FFmpeg is an external runtime dependency and is not bundled, downloaded, or licensed by the app. Its licence depends on the build you install.
• Smart Enhance Upscale uses Apple's on-device VideoToolbox framework when it is supported by the current Mac and macOS. Its availability, supported factors, and model delivery are controlled by the operating system.
• The bundled Noto Sans SC font is licensed under the SIL Open Font License 1.1.

See NOTICE.md for attribution, PRIVACY.md for data handling, and LICENSE for the project license.