version: "1.0.1" description: Edit video with FableCut — assemble a cut, add titles and captions, grade, add transitions, keyframe animation, speed ramps, and export. Use whenever the user wants to cut, trim, caption, subtitle, grade, or otherwise edit a video, or asks to open/start the video editor.

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.

1. `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 with its details read from the file: duration, resolution, frame rate, codecs, audio channels and size. The compact view's MEDIA lines show them for every file (plus tags, favorites and uses:N), so read them there instead of shelling out to ffprobe. Without ffprobe on the machine only the size is known at first; the open editor fills in duration and resolution, so check a field is there before relying on it. To organize the bin, use updateMedia (favorite, tags, folder) and setCollection.

A file marked OFFLINE in the compact view or fablecut_status is missing from media/: find it, put it back under media/ and relinkMedia it — its clips keep their timing. replaceMedia swaps in a different file.

Proxies (fablecut_proxy) only make the preview smoother; export, frames and scopes always use the originals. Make them only when the user asks.

fablecut_projects lists the user's projects and opens, creates or duplicates them; every other tool works on the open one (./project.json). Switch, archive or delete only when the user asks — opening another project changes what they see — and re-read the project after a switch.

Before a big or risky change (restructuring the edit, a remake, a new look on every shot), save a version with fablecut_versions {action:"save", name, note} so the user has a named point to go back to; when they are happy with a cut, save one too. {action:"diff", version} tells you (and them) what changed since. Restore a version only when the user asks.

A project can hold several sequences (timelines sharing its media): the compact view lists them under SEQUENCES, and every op works on the open one. For "a vertical version" or "a 15 s cut-down", add one with {op:"addSequence", name, from:"open", width?, height?} and edit it with {op:"inSequence", sequence, ops:[…]} — the user's editor stays on what they are watching. Open one (openSequence) only when they ask, or to export it.

Things that trip people up

• Cut, ripple, trim and insert with the fablecut_patch_project edit ops

(split, rippleDelete, extract, insert, rippleTrim, roll, slip, slide, crossfade) instead of recomputing start / in by hand — they keep linked audio stems in sync and respect the user's locks.

• 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.

• Grade with the setGrade patch op (props.grade: exposure, temp / tint,

lift / gamma / gain / offset wheels, tone bands, contrast, saturation, tone curves and hue curves; setGradeLayer for a secondary on one colour or one area — check its matte with fablecut_scopes {matte:{clip, layer}}) and check every grade with fablecut_scopes — median luma near 0.35–0.5, no clipped whites, cast strength under ~0.03 on neutral scenes. fablecut_docs {section:"Color"} has the keys and how to read the numbers.

• Motion graphics (shape layers, draw-ons, lower thirds, nulls,

parenting, anchor points, motion paths, compositions, animation presets and templates) have their own skill, motion-graphics, and manual sections ("Shapes, nulls and parenting", "Compositions (nested sequences)" and "Presets and templates" under {section:"schema"}). For a quick lower third or a title that slides in, addTemplate and applyPreset are one op each.

• Export with fablecut_export — the editor's own Fast export, in the

user's open tab or a headless Chrome / Edge. It needs ffmpeg on PATH; it waits for the file and returns its path. For a platform, pass its preset (preset:"youtube", "youtube-shorts", "instagram-reels", "tiktok", "x", "linkedin", "broadcast", "web", "archive") and adjust with delivery:{…} (fps, codec, bitrate, file name, metadata); a 16:9 timeline exported to a vertical preset is cropped from the middle unless the project has an export frame, so say so or set one. fablecut_encode_profiles lists the presets. Several files at once (a master, a YouTube cut, a reel, a square…): outputs:[{preset:"master"}, {preset:"youtube"}, …] renders the timeline once per frame rate and encodes every file from it; setProject {outputs:[…]} saves the list with the project and outputs:true exports it. delivery:{audio:{loudness:-14}} normalizes the mix (−23 for broadcast); the reply checks each file — read it and tell the user about any ⚠ line.