cut-fx 0.1.3

559 named video transitions across four render backends

cut-fx

559 named video transitions across four render backends, with GPU acceleration when available.

Built at Trollfabriken AITrix AB to make programmatic video rendering match the visual vocabulary of consumer video editors. Five-hundred-and-fifty-nine named transitions across eleven taxonomy buckets, mapped to thirty-four hand-written base engines and parametric variants. Four render backends: ffmpeg filter_complex, NumPy/OpenCV procedural, HTML/CSS via web-overlay, and GLSL shaders. GPU acceleration when available, CPU fallback when not. One API: apply_transition(clip_a, clip_b, transition="atomic_teleport", output=...).

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What it solves

Programmatic batch video rendering — AIMOS Insight municipal report videos, civic-education explainers, pipeline-driven content — needs named, repeatable transitions. ffmpeg's xfade covers dissolves. It does not cover 559 named effects. Writing each effect from scratch is not feasible.

Problem	What cut-fx does
Named transitions not in ffmpeg xfade	559 catalog entries map to 34 base engines
Different effects need different render tech	Four backends; catalog picks the right one
GPU present on some machines, absent on others	Runtime detection; CPU fallback always works
LLMs need a machine-readable transition spec	JSON schema export via cut_fx.schema
Beat-aligned cuts require audio analysis	cut_fx.beats wraps audio-arrange
Lyric-timed transitions	Optional lyric-sync integration

---

Installation

pip install cut-fx

Runtime requirement: ffmpeg >= 6.0 must be on PATH.

# Ubuntu / Debian
sudo apt-get install ffmpeg

# macOS
brew install ffmpeg

# Windows
choco install ffmpeg

Extras:

Extra	Installs	Enables
overlay	web-overlay	HTML/CSS/SVG transitions (light_fx, particle_nature, graphic_stylized)
shader	moderngl, moderngl-window	GLSL shader transitions; requires OpenGL 3.3+
beats	audio-arrange, librosa	Beat-synced cut placement
lyrics	lyric-sync	Lyric-timed transitions
all	all of the above	Full feature set
dev	pytest, ruff, build, pillow	Development tools

pip install "cut-fx[overlay,shader,beats]"
pip install "cut-fx[all]"

---

Quick start

from cut_fx import apply_transition

apply_transition(
    clip_a="intro.mp4",
    clip_b="main.mp4",
    transition="atomic_teleport",
    output="combined.mp4",
    overlap_seconds=0.8,
)

List what is available:

from cut_fx import list_transitions, list_categories

list_categories()
# ['motion', 'rotation', 'shape_mask', 'optical_blur', 'light_fx',
#  'particle_nature', 'graphic_stylized', 'digital_glitch',
#  'grid_card_layout', 'film_retro', 'general_fx']

list_transitions(category="digital_glitch")
# ['Capture Glitch 2', 'Console Buzz', 'Cyber Beehive', 'Cyber Flare',
#  'Cyber Phantom', 'Hologram Shred', ...]

Inspect a specific transition:

from cut_fx import get_transition_info

info = get_transition_info("cyber_phantom")
# TransitionInfo(
#     name='Cyber Phantom',
#     slug='cyber_phantom',
#     category='digital_glitch',
#     base_engine='glitch_scan',
#     parameters={'intensity': 0.7, 'scan_lines': 12, 'color_shift': True},
#     backends=['procedural', 'shader'],
# )

---

The catalog

The catalog (cut_fx/data/transitions_catalog.json) lists 559 transition names across 11 taxonomy buckets. Behind those names are 34 base engine implementations. Each base engine accepts parameters: direction, easing, intensity, colour, shape, count, duration curve.

The 559 → 34 design: a named transition is a (base_engine, parameter_set) tuple. Adding a new named variant means adding one JSON entry — no new Python code.

Bucket	Transitions	Base engines	Example named variants
motion	119	4	180 Wipe, Block Slides, Push Right
light_fx	93	5	Basic Flash, Bright Flash, Crescent Sparks
grid_card_layout	47	3	3-block Swing, 3D Card 2, Bizarre Rubik
rotation	46	3	3-flap Turn, 3D Flip, Calendar Flip
shape_mask	44	4	Circle, Comic Cutout, Blast Door
film_retro	35	3	B&W Arrows, Black Smoke, Black Fade
optical_blur	31	3	Auto Focus, Blur & Zoom, Blur Focus
particle_nature	22	3	Bubble Blur, Crystal Energy, Dust Flurry
digital_glitch	16	4	Cyber Phantom, Hologram Shred, Console Buzz
graphic_stylized	12	2	Comic Cut, Glowing Graffiti, Light Graffiti I
general_fx	94	(composed)	3D Glass, Atomic Teleport, Acrylic Fades

The general_fx bucket entries are composed from existing base engines. "Atomic Teleport" is a light_fx flash + shape_mask radial + motion zoom-out, assembled in sequence.

Inspect catalog totals at runtime:

from cut_fx.catalog import catalog_summary

print(catalog_summary())
# {'total': 559, 'categories': 11, 'base_engines': 34, ...}

---

Render engines

Each catalog entry specifies which backend handles it. The dispatch is automatic.

Engine	Handles	Implementation
ffmpeg	motion, rotation, optical_blur, simple wipes	filter_complex with crop/scale/translate/rotate expressions; xfade for cross-dissolves
procedural	digital_glitch, film_retro, custom pixel math	NumPy + OpenCV; frame-by-frame in Python
overlay	light_fx, particle_nature, graphic_stylized, shape_mask	HTML/CSS/SVG via web-overlay; alpha-composited over ffmpeg base
shader	Premium light_fx variants, refraction, fluid sim	GLSL via moderngl; optional; CPU fallback to procedural when absent

The overlay engine requires pip install "cut-fx[overlay]" and a headless Chromium install (playwright install chromium). The shader engine requires pip install "cut-fx[shader]" and OpenGL 3.3+ context support.

Force a specific backend:

apply_transition(
    clip_a="a.mp4",
    clip_b="b.mp4",
    transition="basic_flash",
    output="out.mp4",
    backend="procedural",  # override automatic selection
)

---

Hardware acceleration

At import time, cut_fx probes for hardware encoders and GPU context.

from cut_fx.gpu import gpu_status

print(gpu_status())
# {
#   'ffmpeg_hwaccel': 'nvenc',       # or 'videotoolbox', 'qsv', None
#   'opengl_available': True,
#   'opengl_renderer': 'NVIDIA GeForce RTX 3080',
#   'shader_backend': 'moderngl',    # or 'procedural' (fallback)
# }

Acceleration paths:

• ffmpeg hardware encoders: NVENC (NVIDIA), VideoToolbox (Apple), QSV (Intel). Detected via ffmpeg -hwaccels. Falls back to libx264/libx265 when none is found.
• GLSL shader engine: requires a real GPU context. Falls back to the procedural (NumPy/OpenCV) implementation automatically — output is identical, speed is lower.

Print a summary from the CLI:

cut-fx gpu

No GPU is required. All 559 transitions render on CPU.

---

Beat-synced cuts

Requires pip install "cut-fx[beats]".

from cut_fx.beats import transitions_on_beats

transitions_on_beats(
    clips=["clip1.mp4", "clip2.mp4", "clip3.mp4", "clip4.mp4"],
    audio="track.mp3",
    transition="cyber_phantom",
    output="beat_video.mp4",
    beats_per_cut=2,       # place a cut every 2 beats
    overlap_seconds=0.4,
)

transitions_on_beats uses audio-arrange to extract beat timestamps, then places transitions at beat boundaries. The beats_per_cut parameter controls cut density. Fractional values are supported: beats_per_cut=0.5 cuts on every half-beat.

For lyric-timed cuts, add pip install "cut-fx[lyrics]":

from cut_fx.beats import transitions_on_lyrics

transitions_on_lyrics(
    clips=["verse.mp4", "chorus.mp4"],
    lyrics_file="song.lrc",
    transition="light_burst",
    output="lyric_video.mp4",
)

---

LLM integration

cut_fx.schema exports a JSON Schema describing every valid transition call. Pass it to an LLM as a tool definition.

from cut_fx.schema import transition_spec_schema

schema = transition_spec_schema()
# {
#   "$schema": "https://json-schema.org/draft/2020-12/schema",
#   "title": "TransitionSpec",
#   "type": "object",
#   "properties": {
#     "transition": {"type": "string", "enum": ["atomic_teleport", "cyber_phantom", ...]},
#     "overlap_seconds": {"type": "number", "minimum": 0.1, "maximum": 5.0},
#     "backend": {"type": "string", "enum": ["auto", "ffmpeg", "procedural", "overlay", "shader"]},
#     ...
#   },
#   "required": ["transition"]
# }

Feed the schema to an LLM as a function spec. The LLM returns a valid TransitionSpec object. Pass it directly to apply_transition:

from cut_fx import apply_transition
from cut_fx.config import TransitionConfig

spec = TransitionConfig(**llm_response)
apply_transition(clip_a="a.mp4", clip_b="b.mp4", output="out.mp4", **spec.model_dump())

---

CLI

Apply a transition between two clips:

cut-fx apply intro.mp4 main.mp4 --transition atomic_teleport --output combined.mp4

List all transitions in a category:

cut-fx list --category digital_glitch

List all categories with transition counts:

cut-fx categories

Show detail for a named transition:

cut-fx info cyber_phantom

Render a short preview (3-second synthetic clips):

cut-fx preview atomic_teleport --output preview.mp4

Show GPU and hardware encoder status:

cut-fx gpu

---

Package structure

cut-fx/
├── src/
│   └── cut_fx/
│       ├── __init__.py          # public API re-exports
│       ├── api.py               # apply_transition, apply_sequence, list_*
│       ├── catalog.py           # loads transitions_catalog.json
│       ├── config.py            # TransitionConfig (pydantic model)
│       ├── schema.py            # JSON schema export for LLM tool use
│       ├── gpu.py               # hardware detection
│       ├── beats.py             # beat-synced and lyric-synced cuts
│       ├── cli.py               # cut-fx command-line entry point
│       ├── data/
│       │   ├── transitions_catalog.json   # 559 entries
│       │   └── engine_mapping.json        # slug → base_engine lookup
│       └── engines/
│           ├── base.py          # abstract BaseEngine
│           ├── dispatcher.py    # selects engine per catalog entry
│           ├── ffmpeg/          # filter_complex builder
│           ├── procedural/      # NumPy + OpenCV per-frame
│           ├── overlay/
│           │   └── templates/   # HTML/CSS/SVG transition templates
│           └── shader/
│               └── glsl/        # .vert / .frag shader sources
├── tests/
├── pyproject.toml
├── README.md
└── LICENSE

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© Trollfabriken AITrix AB — MIT licensed