edit-video

Editing video with FableCut

FableCut is a browser video editor whose entire timeline is one JSON document. You edit video by patching that document; the open editor UI hot-reloads within ~150 ms, so the user watches the timeline rebuild as you work.

Start here, every time

1. fablecut_status — starts the editor server if it isn't running and returns the URL, the current project summary, and what's in media/. Call it before anything else. If the user doesn't have a browser tab open, tell them the URL so they can watch.
2. fablecut_docs — the full manual: project.json schema, every prop, transitions, text animations, and a recipe book. Request a single section ({section:"props"}, {section:"Recipes"}) rather than the whole document. Skip it entirely if the schema is already in context.

Making edits

Prefer fablecut_patch_project. It sends only what changes, re-reads the latest document internally, and is merge-safe — it will not clobber a tweak the user just made in the UI. Batch related changes into one call; ops apply in order and bump the revision once.

fablecut_patch_project {ops:[
  {op:"updateClip", id:"c_v2", set:{props:{filterPreset:"teal-orange"}}}
]}

Use fablecut_get_project {compact:true} to plan — it's roughly 10× smaller than the full JSON. Fetch the full document only when you need exact keyframes.

fablecut_set_project replaces the whole document and is conflict-checked: if the user edited in the UI since your last read, it refuses rather than overwriting. On conflict, re-read, re-apply your change, and call it again.

Getting footage in

fablecut_import_media copies a local file into the project and registers it. Media entries may omit duration — the browser probes it and writes it back, so re-read after a moment instead of shelling out to ffprobe.

Things that trip people up

• A cut is just two clips: the first with duration: t, the second with start: +t, in: +t×speed, duration: rest.
• Video and audio clips must satisfy in + duration×speed ≤ media.duration.
• Crossfades are same-track overlap plus transitionIn: {type:"fade"} on the later clip — not a separate object.
• Vary the font per title. Reusing one typeface across a whole edit is the single clearest tell of a machine-made cut; fablecut_docs {section:"Text"} lists the built-in title styles.
• Export is user-driven. The compositor lives in the browser, so you cannot render headlessly. Ask the user to click Export, or run ffmpeg directly against the source files if they just need a file.