Show HN: FableCut – A browser video editor AI agents can drive (zero deps)

FableCut, a browser-based non-linear video editor, exposes its entire timeline as a JSON document, allowing AI agents to edit video via MCP/REST while humans work simultaneously. The zero-dependency tool features Premiere-style editing, keyframe animation, AI background removal, and reference video analysis, with live timeline updates through server-sent events.

A browser video editor that AI agents can drive. FableCut is a Premiere-style non-linear video editor that runs entirely in your browser — and exposes its whole timeline as one JSON document. Edit it by hand, from the UI, or let an AI agent Claude Code, Claude Desktop, or anything that speaks MCP/REST cut your video for you while you watch the timeline update live. Zero npm dependencies. One node server.js . That's it. Most "AI video" tools hide the edit behind an API. FableCut flips that: the project file is the interface . project.json describes media, clips, tracks, effects, keyframes and transitions — any process that can write JSON can edit video, and the open browser UI hot-reloads within ~150 ms via server-sent events. A human and an agent can work on the same timeline at the same time. Editing - 4 video tracks + 3 audio tracks, drag/trim/split/snap, undo/redo Timeline multi-select — rubber-band marquee drag on empty track area , Ctrl/Cmd/Shift+click to add/remove clips, Ctrl+A to select all, Esc to deselect. Drag any selected clip to move the whole group; Delete removes all selected; S splits all selected at the playhead. Inspector shows an "N clips selected" banner.- Beat & cue markers tap M on the beat during playback with edge snapping - Real decoded audio waveforms on clips - Canvas aspect presets 16:9, 9:16 reels, 4:5, 1:1 + safe-area guides Look - 12 one-click filter presets cinematic, teal-orange, noir, vintage, cyberpunk… Adjustment layers — one clip grades everything below it, Premiere-style- Full grade controls: brightness/contrast/saturation/hue, temperature & tint , blur, grayscale/sepia/invert, vignette , animated film grain - Blend modes screen, multiply, overlay… , fit modes contain/cover/stretch , per-edge cropping, corner radius, flip H/V Chroma key green screen with tolerance/softness + spill suppression AI background removal person cut-out, in-browser via MediaPipe Motion - Keyframe animation on ~25 properties with easing Speed ramps — keyframe speed and the engine time-remaps video and the export audio mix the fast-into-slow-mo reel move Camera shake and RGB-split/chromatic aberration , both animatable- 17 transitions: fades, slides, wipes 4 directions , zoom, iris, spin, blur, whip-pan, glitch , pop Text - Kinetic captions: typewriter, word-pop, word-slide, karaoke, letter-pop , wave , bounce , shake Neon glow for that TikTok caption look- Font editor: system fonts, drop-in custom fonts library/fonts/ , and any Google Font by name — loaded automatically - Gradient fills, outline, background pills, letter-spacing, line-height, weights, italic, uppercase, alignment, soft shadows Animated SVG clips - A first-class svg clip kind: CSS- @keyframes -animated SVGs render frame-accurately in preview and export the compositor freezes the animation at any time . Agents can author their own vector overlays — lower-thirds, confetti, sparkles — as plain .svg files. Starters included. Remake a reference video - Give it a reference edit a reel you like and get back an edit blueprint : shot boundaries, music beats + BPM, a loudness curve, per-shot energy, the drop — plus the reference's music track extracted into your media, ready to rebuild the same idea with your own footage. Zero extra dependencies ffmpeg does the decoding; onset/tempo detection is plain Node . node analyze.js ref.mp4 , POST /api/analyze , or the fablecut analyze reference MCP tool. Asset library library/ folders surface as tabs in the UI: Elements overlay art , Sound FX , SVG — drop files in, the open editor refreshes live Export - Fast export: browser renders every frame + an offline audio mix, ffmpeg encodes a frame-accurate CRF-18 MP4 keeps rendering if you switch tabs - Realtime MediaRecorder fallback when ffmpeg isn't available git clone https://github.com/ronak-create/FableCut.git cd FableCut node server.js → http://localhost:7777 Requirements: Node 18+ and a Chromium-based browser. ffmpeg on PATH is optional but recommended fast export + upload remuxing . AI background removal fetches its model from a CDN on first use. Drop media into the window or ./media/ , drag clips onto the timeline, edit, export. Everything an agent needs is in CLAUDE.md — the complete schema, semantics and recipes. Point any capable model at that file and it can operate the editor end to end. Three equivalent control surfaces: - MCP best for Claude Code / Claude Desktop — register the bundled zero-dependency MCP server once: claude mcp add -s user fablecut -- node "<path-to /fablecut/mcp-server.js" Tools: fablecut status auto-starts the editor , fablecut docs , fablecut get project , fablecut set project , fablecut patch project , fablecut import media , fablecut analyze reference .The surface is token-efficient by design : agents patch the timeline with small ops fablecut patch project instead of round-tripping the whole document, read a compact one-line-per-clip summary fablecut get project {compact:true} , and fetch only the manual sections they need fablecut docs {section:"props"} . - The file — read project.json , modify, bump revision , write. The UI live-reloads. - REST — GET/PUT /api/project , POST /api/upload , GET /api/library , SSE at /api/events . See CLAUDE.md for the full list. Example: ask Claude Code "cut these six clips to the beat markers, add a teal-orange grade, put a word-pop caption on top and a whoosh on every cut" — and watch the timeline rebuild itself. Or hand it a reference: "here's a reel I like — analyze it and remake it with my clips, same music" . The agent calls fablecut analyze reference , gets the blueprint cuts, beats, BPM, energy, drop, extracted music , and rebuilds the structure shot-for-shot with your footage. Conflict-safe concurrent editing : the UI, the MCP tools, and direct project.json writes all agree on a revision counter. If you edit a clip in the UI while an agent is mid-task, the agent's next write is rejected 409 from the REST API / a conflict error from fablecut set project instead of silently overwriting your change. The UI similarly detects when an agent write supersedes a not-yet-saved local tweak and tells you with a toast instead of dropping it silently. server.js zero-dependency HTTP server: static hosting, REST API, SSE, ffmpeg export pipeline app.js the editor: timeline UI, compositor, keyframes, text engine, SVG rasterizer, chroma key, exporters index.html single-page UI style.css dark editor theme mcp-server.js stdio MCP server exposing the editor to AI agents analyze.js reference-video analyzer: shots, beats/BPM, energy, drop, music extraction module + CLI CLAUDE.md the agent manual schema + recipes — also served by fablecut docs project.json your timeline created on first run; gitignored media/ project footage gitignored analysis/ cached edit blueprints from /api/analyze gitignored library/ default assets: elements/ sfx/ svg/ fonts/ exports/ finished renders gitignored SVGs animate with plain CSS @keyframes . One convention: never hardcode animation-delay — set --d: 0.4s instead, and the compositor drives time by pausing all animations and rebasing their delays. Full rules + a skeleton in CLAUDE.md /ronak-create/FableCut/blob/main/CLAUDE.md authoring-animated-svgs-the-svg-clip-kind ; working examples in library/svg/ /ronak-create/FableCut/blob/main/library/svg . - The repo ships with 20 Google Fonts library/fonts/ , OFL — see LICENSES.md there and a set of self-authored SVG overlays and animated elements library/elements/ , library/svg/ , MIT like the rest of the repo . library/sfx/ is yours to fill gitignored : sound-effect sites typically don't allow redistributing their files in a public repo, so FableCut doesn't — library/sfx/README.md lists good free sources.- Export runs in the browser because the compositor is the browser; agents ask you to click Export or render directly with ffmpeg from media/ .