# FFmpeg xfade Chain for N Clips — effect skill for transitions

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Chain xfade + acrossfade across N clips; offset of the k-th transition = d1+…+dk − k·T.

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

## What it does

Every join gets the same transition; total length = sum of clip durations − (N−1)·T.

**When:** Batch slideshows, AI-shot sequences and reels where an agent must join many clips with transitions in one render.

**Watch out:** Offsets computed from the source clips instead of the running output; and clips shorter than T.

**Timing:** T usually 0.3–1.0 s; same T for every join keeps the math simple

**Also called:** xfade offset math, chained xfade, acrossfade chain, slideshow transitions

### In FFmpeg

Each xfade's offset is measured on its first input, which is the output of the previous xfade (already shortened by (k−1)·T). So offset_k = (d1 + … + dk) − k·T. `acrossfade` overlaps audio by the same T, keeping it in sync.
```bash
#!/usr/bin/env bash
# xfade-chain.sh <transition> <T> out.mp4 clip1 clip2 [clip3 ...]   (tested with ffmpeg 8.1)
set -euo pipefail
TR=$1; T=$2; OUT=$3; shift 3
W=1080; H=1920; FPS=30; n=$#; i=0; off=0; f=""; inputs=()
for c in "$@"; do
  inputs+=(-i "$c")
  f+="[$i:v]fps=$FPS,scale=$W:$H:force_original_aspect_ratio=decrease,pad=$W:$H:(ow-iw)/2:(oh-ih)/2,setsar=1,format=yuv420p,settb=AVTB,setpts=PTS-STARTPTS[v$i];"
  f+="[$i:a]aresample=48000,aformat=channel_layouts=stereo,asetpts=PTS-STARTPTS[a$i];"
  i=$((i+1))
done
vp=v0; ap=a0; i=1
for c in "${@:1:$((n-1))}"; do
  d=$(ffprobe -v error -show_entries format=duration -of csv=p=0 "$c")
  off=$(echo "$off + $d - $T" | bc -l)            # offset_k = d1+..+dk - k*T
  f+="[$vp][v$i]xfade=transition=$TR:duration=$T:offset=$off[vx$i];"
  f+="[$ap][a$i]acrossfade=d=$T[ax$i];"
  vp=vx$i; ap=ax$i; i=$((i+1))
done
ffmpeg -y "${inputs[@]}" -filter_complex "${f%;}" -map "[$vp]" -map "[$ap]" \
  -c:v libx264 -crf 18 -pix_fmt yuv420p -c:a aac -movflags +faststart "$OUT"
```
Tested: 5 s + 4 s + 6 s with T = 0.5 → 14.0 s output.

### Where this comes from

- [FFmpeg filters: xfade](https://ffmpeg.org/ffmpeg-filters.html#xfade)
- [FFmpeg filters: acrossfade](https://ffmpeg.org/ffmpeg-filters.html#acrossfade)
- [FFmpeg filters: settb](https://ffmpeg.org/ffmpeg-filters.html#settb_002c-asettb)

## Use when

- Batch slideshows, AI-shot sequences and reels where an agent must join many clips with transitions in one render.

## Not for

- Offsets computed from the source clips instead of the running output; and clips shorter than T.

## 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/4f24964231a8/take-ffmpeg-xfade-chain.mp4 — fade between two shots, with the timeline strip of the edit. Footage: Coffee Run (2020), Blender Studio | studio.blender.org, CC BY 4.0; Coffee Run (2020), Blender Studio | studio.blender.org, CC BY 4.0. (credit: Rendered by varg · Coffee Run (2020))

## 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.