# MoviePy Crossfade and Slide — effect skill for transitions

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In MoviePy v2, crossfade with vfx.CrossFadeIn plus negative padding (or with_start in a CompositeVideoClip).

- **Type:** [Effect](https://varg.ai/how-to/effects.md) · [Transitions](https://varg.ai/how-to/browse/skills/transitions.md)
- **Slug:** `moviepy-crossfade`
- **Status:** live
- **Publisher:** varg (varg, verified)
- **License:** MIT
- **Source:** https://github.com/vargHQ/skills/blob/main/varg-video-edit-library/references/transitions.md#moviepy-crossfade
- **Works in:** Claude Code, Claude.ai, Codex, Cursor, OpenClaw, Gemini CLI, Any MCP client, varg Studio
- **Requires:** Python + MoviePy
- **Cost:** Free — the take renders locally; generated footage, if any, bills by the model

## What it does

Crossfades and simple slide-ins from Python.

**When:** Python pipelines that already use MoviePy; quick prototypes.

**Watch out:** v1 syntax (`crossfadein`, `set_start`, `subclip`) on MoviePy 2.x; and slow renders of long timelines.

**Timing:** Any; T = 0.5 s in the example

**Also called:** moviepy, CrossFadeIn, concatenate_videoclips padding, CompositeVideoClip

### In MoviePy

Tested with MoviePy 2.2.1 (5 s + 4 s, T = 0.5 → 8.5 s):
```python
from moviepy import VideoFileClip, CompositeVideoClip, concatenate_videoclips, vfx, afx
T = 0.5
a = VideoFileClip('a.mp4').subclipped(0, 5).with_effects([afx.AudioFadeOut(T)])
b = VideoFileClip('b.mp4').subclipped(0, 4).with_effects([vfx.CrossFadeIn(T), afx.AudioFadeIn(T)])
out = concatenate_videoclips([a, b], method='compose', padding=-T)
# same thing explicitly:
# out = CompositeVideoClip([a, b.with_start(a.duration - T)])
out.write_videofile('out.mp4', fps=30)
```
`CrossFadeIn` only works inside a composite (it fades the clip's mask). Other effects: `vfx.SlideIn(duration, side)`, `vfx.SlideOut`, `vfx.FadeIn/FadeOut` (through black), `vfx.Freeze`, `vfx.MultiplySpeed`.

### Where this comes from

- [MoviePy v2 video effects (CrossFadeIn, SlideIn)](https://github.com/Zulko/moviepy/tree/master/moviepy/video/fx)

## Use when

- Python pipelines that already use MoviePy; quick prototypes.

## Not for

- v1 syntax (`crossfadein`, `set_start`, `subclip`) on MoviePy 2.x; and slow renders of long timelines.

## Install

- Claude Code: `claude plugin marketplace add vargHQ/skills && claude plugin install varg@varg`
- Codex: `npx skills add vargHQ/skills --skill varg-video-edit-library -a codex -y`
- Cursor: `npx skills add vargHQ/skills --skill varg-video-edit-library -a cursor -y`

## Example output

https://s3.varg.ai/how-to/previews/4f0134d407bb/take-moviepy-crossfade.mp4 — slideright between two shots, with the timeline strip of the edit. Footage: Sprite Fright (2021), Blender Studio | studio.blender.org, CC BY 4.0; WING IT! (2023), Blender Studio | studio.blender.org, CC BY 4.0. (credit: Rendered by varg · Sprite Fright (2021) + WING IT! (2023))

## More transitions skills

- [editly](https://varg.ai/how-to/skills/editly.md): Declarative JSON5 video editing CLI/API: clips, titles, transitions, audio mixing, rendered with ffmpeg.
- [Mix (Cross Dissolve)](https://varg.ai/how-to/skills/mix-dissolve.md): The two shots blend through each other. The quietest transition: "time passes" or "this continues".
- [Dip to Black](https://varg.ai/how-to/skills/black-fade.md): A fades to black, then B fades up. Marks the end of a section or a bigger jump in time.
- [White Flash](https://varg.ai/how-to/skills/white-flash.md): The frame blows out to white for a moment and opens on the next shot. Energy, memory or a camera snap.
- [Pull In (Zoom In)](https://varg.ai/how-to/skills/pull-in-zoom.md): The camera rushes into shot A and lands, still moving forward, in shot B. The signature short-form transition.
- [Pull Out (Zoom Out)](https://varg.ai/how-to/skills/pull-out-zoom.md): The camera jerks backwards out of shot A and keeps pulling back as shot B settles in.