FableCut

A browser video editor that AI agents can drive.

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https://github.com/user-attachments/assets/2430b854-168b-4a9a-af2e-489e5efa7543

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.

Why it's interesting

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.

Features

Editing

• Video + audio tracks (default 3+4; add more with +V / +A in the track header; right-click an empty header → Remove track), drag/trim/split/snap, undo/redo
• Settings (cog in the top bar) — optional prefs stored in this browser via localStorage. Enable Link timeline and Project bin selection so picking a timeline clip highlights its media in Project, and clicking a Project item selects every timeline clip that uses it (off by default).
• Video + audio tracks (default 3+4), drag/trim/split/snap, undo/redo
  • +V / +A in the track header add a video or audio lane (up to 16 each)
  • Right-click an empty track header → Remove track (disabled if the lane has clips, or if it would leave you with zero video/audio tracks)
  • Track header S solos that lane (mutes all others); click again to restore the previous mute state. Using the mute toggle while soloed exits solo.
  • Track targeting — click a track's name to target / untarget it (lit = targeted). Split, insert, ripple, close gap and jump-to-cut touch targeted tracks only; the eye / speaker toggle is output-only (hide from preview and export) and no longer blocks edits. A selected clip is edited wherever it sits.
  • Track lock — the padlock in the track header. Nothing on a locked track can be moved, trimmed, split or deleted, and ripples leave it in place while the other tracks shift — lock the music bed and re-cut the picture freely.
• Clip lock, disable and unlink — right-click a clip (or use the toggles at the top of the inspector): Lock pins it like a locked track; Disable (⇧E) keeps it on the timeline but hides it from preview and export; Unlink (Ctrl/Cmd+L) splits a video from its audio so they move separately, and Link re-joins them once they line up again. Agents see locks too: fablecut_patch_project refuses to edit locked clips unless the op says force: true.
  • Dropping a video with more audio channels than A-tracks adds the missing lanes automatically (up to 16) and toasts how many were added; each channel becomes a linked stem on its own A-track
• Direct manipulation on the monitor — click a clip or title on the preview to move, resize (corner handles), or rotate (top handle, Shift-snap) it directly
• 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) — name and colour them, drag them on the ruler, jump with ⇧m / Alt+⇧m or the Markers list; snapping targets (clip edges, playhead, markers, IN/OUT, keyframes, frame grid) are picked from the ▾ beside Snap
• Press Alt+t to add an in/out transition based on the playhead position over the selected clip. The last used transition is remembered as the default. Drag the overlay triangle to adjust duration; Delete clears the focused transition.
• Real decoded audio waveforms on clips
• Mixer — the Mixer tab beside the Inspector has a strip per audio track (fader, pan, mute, solo, meter) and a master fader with a live LUFS readout. Preview and export run through the same mix, so what you hear is what renders.
• Clip gain, channels and Normalize — each audio clip has a Gain (dB, before volume and keyframes), a Channels mode (stereo, mono, left, right, swap) and Normalize: measure the selected clips (ITU-R BS.1770 loudness or sample peak) and set their gain to hit −14 / −16 / −23 LUFS or −1 dBFS. Linked stems share one gain so a stereo pair stays balanced.
• Volume line, fades and crossfades — every audio clip shows its volume as a line you drag; Ctrl/Cmd-click adds a keyframe, Alt-click removes one. Corner grips drag fades in and out, drawn with their real curve (constant power, constant gain or exponential). Shift+D crossfades the cut next to the selection, borrowing spare media from both sides so nothing else moves.
• Auto-duck — select the music, pick the dialogue track and an amount, and the music dips wherever someone speaks (ramping down just before, back up after). It rides on top of the music's own volume, so re-running or clearing it never touches your levels. Agents use fablecut_auto_duck.
• Audio effects and presets — EQ, high/low-pass, compressor, limiter, noise gate, delay, reverb, distortion, stereo width and pitch shift, chained per clip, per track (Mixer → FX), per bus and on the master. Presets: Clean voice, Podcast, Radio, Deep voice, Telephone, Cinematic, Wide and Muffled, all tweakable afterwards. Preview and export run the same effects. Agents use the setFx patch op.
• Effect automation — the ◆ beside an effect setting keys it at the playhead, like clip keyframes: sweep a filter into the drop, open up a reverb at the end. Agents use setFxKeys.
• Submix buses — + Bus in the Mixer adds a bus with its own effects, fader, pan, mute and meter; route tracks into it from the menu under each track's name (all the dialogue through one compressor and one fader).
• Noise reduction — the inspector's Noise control (Light / Medium / Strong) measures the file's noise floor and renders a cleaned copy with ffmpeg; the clip's audio switches to it and Off switches back. Agents use fablecut_denoise.
• Project bin folders — tree view with expand/collapse; drag media or folders to nest; right-click the Project tab → New folder; drop files onto a folder to import into it
• Import from URL — + URL downloads an HTTPS video/audio/image into ./media/ (same-origin after import). Remote SVG is refused. Agents use fablecut_import_media with an https:// path. The URL is not kept as media.src — that would taint the canvas and break export.
• Audio Hold — timeline toolbar toggle: while paused, loops one frame of audio at the playhead (useful when stepping frame-by-frame). Scrubbing or frame-step retargets the held slice; meters stay live. Play / Pause turns it off.
• Canvas aspect presets (16:9, 9:16 reels, 4:5, 1:1) + project FPS select (24 / 25 / 30 / 50 / 60; non-preset rates show as Custom) + safe-area guides
• Export frame / reframing — composition canvas can be larger than the delivery crop (exportFrame in project.json). Preview dims the overscan; drag the Export frame handle to reframe (e.g. 16:9 canvas → 9:16 export). Fast export crops to the frame; WebCodecs and Realtime export are disabled while a frame is set
• Program Monitor zoom — mouse-wheel over the preview zooms the composition toward the cursor (fit → up to 2 screen pixels per canvas pixel). Magnified view uses *