FableCut

A browser video editor that AI agents can drive.

English · 简体中文 · 日本語 · Español · Português (BR)

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.

Sponsors

[Sidrune AI](https://fluxionai.space/register?source=github&campaign=github-sidrune-fablecut&promo=SDRFABLECUT) — One API for GPT, Claude, and other leading AI models. Sign up and get $3 in API credit.

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.

Taking back what the agent did. Every agent edit is one undo step of its own: Ctrl+Z takes back the agent's last change first (and says so), then goes on to yours, so the two never get mixed. For bigger rollbacks there are Versions: one is kept when an agent starts editing (again at most every 10 minutes while it works), before it rewrites the whole project, before every big operation (cutting silences, snapping to the beat, reframing), and every 10 minutes while you edit. Restore one from the Versions panel, or ask the agent (fablecut_versions), and compare any version with now first.

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.
• Reframe — make a 9:16, 1:1 or 4:5 copy of your edit whose shots follow the subject: a virtual camera pans after what matters in each shot and writes ordinary position keys you can still edit. From New sequence… or the Inspector's Reframe section; agents use fablecut_reframe.
• Highlights — the best moments of long footage (movement, sound, a clear picture) cut into a short edit in a new sequence, in story order and never across a cut. From the sequence menu's Highlights…; agents use fablecut_highlights.
• Silence removal — the inspector's Silence section (or right-click → Find silences) listens to a take and marks every pause on the timeline; Cut extracts them all in one undo step, keeping a little quiet beside each phrase so words aren't clipped. Agents use fablecut_silence.
• Beats — the inspector's Beats section finds a music clip's tempo, a steady beat grid and the drop, and shows the beat across the timeline. Mark the beats, snap every cut onto the nearest one, or re-cut a track so each shot lasts 1, 2, 4, 8 or 16 beats. Agents use fablecut_beats.
• Transcripts and text-based editing — the Transcript tab turns speech into words with times, in the browser (Whisper; the model downloads once and the audio never leaves your machine). Click a word to go there, select words and press Delete to cut them, or find a phrase and cut every time it is said. Agents use fablecut_transcribe to read an interview, find a line and cut it.
• Captions — one click makes captions from the transcript, timed word by word: subtitle, karaoke, a highlighted word or big popping words, sized for the canvas. Export or import SRT and WebVTT. Agents use fablecut_captions.
• 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
• Media management — each file's frame rate, codecs, audio channels and size (ffprobe); search by name, codec, resolution or #tag; filter by favorites, used / unused, kind, tag or collectio