Cut a tutorial video in an undocumented editor by writing its project file

Settakarn Kl wanted Claude Code to edit screen recordings in FilmCraft, an early open-source video editor written in Rust. FilmCraft has no editing API and no published schema for its .fcproj project files, which are plain JSON. Claude found an undocumented --control flag that starts a local server for driving the app's UI. On a copy of the project it told the app to do things like drag a clip onto the timeline, then read the recovery snapshots the app saves every five seconds to learn the real field names. From that it wrote a timeline writer and a launcher that opens the app to prove a file loads, and bundled both into a Claude Code skill. In use, the author imports footage, closes the app and gives a brief such as a five minute tutorial split by steps, Thai captions on each step and loading waits sped up 3x. Claude uses ffmpeg to find scene changes and pull stills, writes a JSON edit plan, writes the timeline after backing up the file, then opens FilmCraft, counts clips, checks the log and returns a screenshot.

The author shows a finished tutorial video and the resulting sequence open in FilmCraft. Change requests in plain words, such as speeding up the intro to 2x or trimming the whole cut under three minutes, go through the edit plan and are recalculated from the original clip lengths, so speeds do not stack. It handles straight cuts only. Transitions and titles are left out because their schema was never confirmed. Thai text renders in the exported video but shows as empty boxes in the app's UI. No time or cost figures are given.

Close FilmCraft before Claude writes the file, or the app saves over its work. The skill targets FilmCraft 0.14.x with schema version 15 on macOS with Python 3 and ffmpeg, and the new sequence lands in a bin that you open by hand. The post is in Thai and the skill is published on GitHub.