FlyingMouse Format: an offline Windows converter that bundles its own engines

The offline constraint FlyingMouse Format is built around

Most browser-based converters require you to upload the file to someone else's server. FlyingMouse Format takes the opposite position: the README states that FFmpeg, LibreOffice, Poppler and Tesseract are bundled inside the application, and that conversion runs locally. For anyone handling contracts, medical scans, internal spreadsheets or camera RAW files under a policy that forbids third-party uploads, that single property is the reason to look at the project at all.

The audience is narrower than the feature list suggests. The README describes a Windows 10/11 build, a Windows 7 SP1 Legacy build, and macOS 11+ builds for Apple Silicon and Intel. The interface is Chinese and English, with the first launch following the system language. The author is identified as 牢蜂 (LaoFeng), and the README carries a non-commercial notice: personal free use only, with resale, repackaging or rebranding prohibited. That is a distribution constraint, not a technical one, and it rules the project out for anything you charge for.

How the conversion pipeline is assembled from separate engines

The repository layout shows the app is not one converter but a dispatcher over several. Top-level files such as office-convert.js, office-engine.js, office-runtime.js, pdf.js, pdf-structure-engine.js, pdf-table-extractor.js, media.js, image.js, ocr.js and ebook.js each own a format family, and bin/ holds the native engines. The README states that Windows 10/11 and macOS builds add Pandoc for document work, while the Win7 Legacy build does not, which is why Markdown to Word and Markdown to PDF are unavailable there.

Conversion quality is handled with explicit fallbacks rather than silent success. For PDF to Word, the README says the Windows 10/11 build prefers a layout engine, checks text coverage before accepting the result, and processes mixed scanned pages page by page; degraded rebuilds and OCR are labelled. For PDF to Excel, it describes electronic text coordinates, scanned-page OCR, bordered and borderless tables, multi-table and cross-page continuation, merged cells, low-confidence annotations and a Raw fallback. The README also states that complex multi-column layouts, image positioning and scanned punctuation are not guaranteed to match the original PDF. That is an honest boundary, and it is the part to read before promising a colleague a perfect round trip.

Resource limits are enforced rather than documented as advice. The README states that advanced PDF structure recognition is capped at 500 pages, 50 million pixels per page and 100 million cumulative pixels at 144 DPI, with an explicit message when a file exceeds them. Audio support has a hard edge too: ordinary formats such as MP3, WAV, FLAC, M4A, AAC, OGG, OPUS and WMA convert, but the README states that encrypted platform formats including NCM, KGG, mflac, kgma and kwm are not supported inputs.

Installing FlyingMouse Format and running a first conversion

The README points ordinary users at the Releases page rather than the source tree, because the repository does not contain the large FFmpeg, LibreOffice, Poppler and Tesseract binaries. Download the installer for your platform and version from that page, install it, then drag a file in, pick a target format and choose where to save. The app remembers the target per source extension and remembers the last save directory.

If you prefer the command line, the repository ships cli.js, and the README gives these examples. The first command reports which conversions the local engines can actually perform, which is worth running before scripting anything, because capability depends on which engine binaries are present.

node cli.js capabilities --json
node cli.js targets example.pdf --json
node cli.js convert input.docx --to pdf --output output.pdf --json

Batch work and the two PDF assembly commands follow the same shape. The README shows a multi-file conversion into a directory, plus image-to-PDF and PDF merge helpers.

node cli.js convert a.png b.png --to webp --output-dir converted --json
node cli.js images-to-pdf 1.jpg 2.jpg --output album.pdf --json
node cli.js merge-pdfs a.pdf b.pdf --output merged.pdf --json

An installed build can be driven the same way through the application entry point: the README gives `FlyingMouse Format.app/Contents/MacOS/FlyingMouse Format --cli ...` on macOS and `FlyingMouse Format.exe --cli ...` on Windows. There is also an in-app "接入 Agent" button that looks for existing `~/.codex/skills`, `~/.claude/skills` or `~/.agents/skills` directories and installs the bundled skill after confirmation; the README states it will not create directories for products you have not installed.

Building from source requires the engines to be supplied by you. The README says to prepare the resources under `bin/` before the full conversion feature set works.

npm install
npm run desktop

Where FlyingMouse Format stops being the right tool

The licence is the first wall. The README states the software is for personal free use only, and prohibits commercial sale, resale and repackaging. If your use case is a paid service, an internal product you sell, or a rebranded distribution, this project is not available to you regardless of how well it converts files.

The second wall is platform readiness. The README describes 0.7.3 as a local Windows x64 repair candidate and says the public availability of installers depends on the Release assets. It states that the Windows 7 Legacy build was not built in that round and that both macOS architectures had not been packaged, with real-device acceptance still pending. It also says Windows installers are unsigned, so SmartScreen may warn, and macOS builds are unsigned and not notarized, so Gatekeeper may block them. Treat the README's version table as a statement of intent, and the Releases page as the actual inventory.

The third wall is the Legacy build's dependency position. The README states the Win7 build pins Electron 22.3.27, Sharp 0.32.6 and PDF.js 2.16.105, that Electron 22 is no longer maintained upstream for security, and that it carries known dependency risks that cannot be upgraded on Windows 7. It notes PDF.js dynamic code execution is mitigated with `isEvalSupported: false`, and recommends offline processing of trusted files only. That is a real reduction in safety margin, not a footnote.

Finally, the format list has holes. Encrypted music-platform audio is refused by design, AV3A is out of scope, and the README itself says complex multi-column PDFs, image positioning and scanned punctuation may not survive a PDF to Word round trip intact.

How FlyingMouse Format differs from LibreOffice and Pandoc used directly

The obvious alternative is to install the engines yourself: LibreOffice for Office and PDF work, FFmpeg for media, Poppler for PDF text and images, Tesseract for OCR, Pandoc for Markdown. That stack is more capable in the long run, because you control versions and can script anything, and none of it restricts you to personal use. The difference in approach is that FlyingMouse Format pre-assembles those engines behind one UI, one CLI and one set of remembered preferences, and adds the parts the raw tools do not have: a batch queue with per-file progress and failure reasons, a preview drawer for images, PDFs, text, audio and video, and the PDF-to-Excel table extraction path with coordinate, OCR and Raw fallbacks.

A second alternative is a hosted converter. Those remove the installation step entirely, but they require uploading the file, which is precisely the property FlyingMouse Format was built to avoid. If your files are public and small, a hosted tool is less work. If they are not, the offline requirement decides the question before feature comparison starts.

The honest framing is that FlyingMouse Format is a convenience layer with a licence and a platform story attached. If you already maintain a scripted LibreOffice and FFmpeg pipeline that your team trusts, this project does not replace it. It replaces the case where a non-technical colleague needs to turn a folder of HEIC photos into JPGs, or a scanned PDF into a spreadsheet, on a machine with no network.

Maintenance, upgrade cost and what the licence actually gates

The repository is not archived, and the last push was on 2026-09-14. The release list shows v0.5.4, v0.5.5 and v0.6.5 published in August and September 2026, with the package version at 0.7.3. Version numbers in this project do not move monotonically across the README and the release list, so read the asset name rather than the tag when deciding what you are installing.

Upgrade cost comes from the bundled engines. Every Electron, Sharp, PDF.js and Pandoc change is an application release, and the Win7 Legacy line is frozen at Electron 22.3.27 because newer Electron does not run on Windows 7. The README also notes that the source repository excludes the large engine binaries, so a source build requires you to source and place them under `bin/` yourself, and the Win7 staging path uses a dedicated `win7-package-lock.json` rebuilt with `npm ci` and a Node.js version in the 18 to 22 range; other major versions are rejected before staging is modified.

On licensing: the repository carries a LICENSE file and a THIRD_PARTY_NOTICES.md, and the README states the application is non-commercial personal use only. The bundled FFmpeg, LibreOffice, Poppler, Tesseract and Pandoc each carry their own licences, and the README does not summarize them. If you plan to redistribute anything, read LICENSE and THIRD_PARTY_NOTICES.md in full; this is a description of what the repository contains, not legal advice.

Editorial conclusion

Adopt FlyingMouse Format if you convert files on a Windows 10 or 11 machine that cannot reach the internet, and you accept the personal-use-only licence. Do not adopt it for a commercial service, for encrypted music-platform audio, or for a Windows 7 fleet, because the Legacy build uses Electron 22.3.27 which the README says is no longer maintained upstream. Before relying on it, verify on the Releases page which 0.7.3 assets actually exist, since the README states the Win7 and both macOS packages were not built at the time of writing, and check whether the unsigned installer triggers SmartScreen on your machine.

Frequently asked questions

Official sources

1. Issues
2. LaoFeng-mouse/flyingmouse-format on GitHub
3. README
4. Releases