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

• 3 video tracks + 4 audio tracks, 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).
• 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), <kbd>Ctrl/Cmd/Shift+click</kbd> to add/remove clips, <kbd>Ctrl+A</kbd> to select all, <kbd>Esc</kbd> to deselect. Drag any selected clip to move the whole group; <kbd>Delete</kbd> removes all selected; <kbd>S</kbd> splits all selected at the playhead. Inspector shows an "N clips selected" banner.
• Beat & cue markers (tap <kbd>⇧m</kbd> on the beat during playback) with edge snapping
• Press <kbd>Alt+t</kbd> 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; <kbd>Delete</kbd> clears the focused transition.
• Real decoded audio waveforms on clips
• 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
• 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
• 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 native scrollbars so overflow stays reachable; middle-click or <kbd>Alt</kbd>+drag pans. The Fit button (shown while zoomed) resets to the fit-to-stage baseline
• Preview playback speed — shuttle the monitor through 1×/1.5×/2×/4× with J/K/L (from a stop <kbd>J</kbd>/<kbd>L</kbd> start playback; while playing <kbd>L</kbd> steps faster and <kbd>J</kbd> slower, <kbd>K</kbd> toggles play/pause and resets to 1×); affects the preview player only, never the export
• Resizable workspace: drag the divider between monitor and timeline (double-click resets), plus S/M/L timeline track-density presets (S hides thumbnails for compact tracks)
• Zoom to selection (<kbd>⇧Z</kbd>) frames all selected clips, not just one
• IN/OUT work area — set markers with <kbd>i</kbd> and <kbd>o</kbd> (<kbd>⇧I</kbd> / <kbd>⇧O</kbd> to clear). Enabling Limit constrains playback to the marked range and maps <kbd>Home</kbd> / <kbd>End</kbd> to the IN and OUT positions rather than the full timeline. <kbd>t</kbd> splits clips at the markers; <kbd>⇧t</kbd> trims clips to the work (between marker in and marker out) area.
• Find & close gaps — a gap is a stretch where every enabled track is empty (black frames). <kbd>g</kbd> jumps the playhead to the next shared gap (wraps; respects IN/OUT when both are set). <kbd>⇧G</kbd> closes the gap under the playhead by pulling later clips left on all enabled tracks.
• Reset a property — <kbd>Ctrl/Cmd+click</kbd> an inspector label to restore that effect/prop to its default (paired fields like Crop L/R reset together). Matching keyframes for the prop are cleared too; transition labels clear the in/out transition.
• Replace media — the inspector's Source button (any video/audio/image/svg clip) swaps the underlying file while keeping position, trim, keyframes, transitions and every effect. Pick another item already in the bin or Browse file… to import and replace in one step. A video's linked L/R audio companions are swapped along with it; a shorter replacement clamps the trim to fit and toasts that it did so.
• Multi-channel video audio — a video with more than 2 audio channels gets a linked audio clip per channel, not just L/R (5.1, 7.1…). Extra audio tracks (A5, A6, …, capped at 16) are created automatically as needed; replacing a clip's media re-syncs the linked channel clips to the new source's channel count, adding/dropping extras and new tracks as needed.

Look

• 14 one-click filter presets (cinematic, teal-orange, noir, vintage, cyberpunk, sunset, midnight…)
• 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
• Keyframe markers on clips — diamonds on the clip body at each unique keyframe time (tooltip lists channels; a count badge when several share a time). <kbd>Ctrl/Cmd+←</kbd> / <kbd>Ctrl/Cmd+→</kbd> jumps the playhead to the previous / next keyframe (selected clips first, else clips under the playhead)
• Keyframe graphs — toggle a property’s curve in the inspector to show an interpolated value graph beside the program monitor; click the graph to seek
• 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

• Title styles — one-tap cohesive looks (Impact, Elegant, Kinetic cut, Neon, Handwritten, Luxury, and more); new titles vary the font, placement and animation automatically instead of defaulting to one flat style
• Kinetic captions: typewriter, word-pop, word-slide, karaoke, letter-pop, wave, bounce, shake, clip-reveal, zoom-in, font-cut (rhythmic typeface cuts), rise-mask
• 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, soft shadows
• Text layout — horizontal Align: left / center / right / justify (extra spaces between words). Drag a title’s corner handles to create a text box (boxW / boxH); further corner drags resize it (opposite corner stays fixed; <kbd>Ctrl/Cmd</kbd> resizes from center; <kbd>Shift</kbd> locks aspect). Inside a box, text wraps at the fixed font size by default; enable Scale to fit to shrink the font so the whole block fits. V-align (top / middle / bottom) places the text block vertically in the box. Set Box W/H to 0 to return to hug-content sizing.

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 v