beat-sync-video-editing

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---
name: beat-sync-video-editing
description: This skill should be used when the user asks to "edit a video to music", "create a beat-synced edit", "make a montage", "sync cuts to beats", "cut a video to the beat", "make a music video edit", "edit clips to a song", "build FFmpeg filters for video editing", or mentions combining video clips with audio tracks using timed cuts. Provides knowledge of the EditPlan format, FFmpeg filter_complex construction, and beat-sync editing workflows.
---

# Beat-Sync Video Editing

## Purpose

Provide domain expertise for creating beat-synced video edits: taking a source video and an audio track, selecting clips from the video that align with the music's rhythm, and rendering the final output with FFmpeg.

## Core Concept: The EditPlan

Every edit starts as an EditPlan — a JSON structure that describes which video clips to use and where in the audio to place them:

```json
{
  "audio_start": "00:13",
  "audio_duration": 6.5,
  "clips": [
    { "video_start": "00:08", "duration": 2.0, "description": "Opening shot" },
    { "video_start": "00:45", "duration": 1.5, "description": "Action moment" },
    { "video_start": "01:22", "duration": 3.0, "description": "Build-up" }
  ],
  "reasoning": "Matches rising intensity with beat drops"
}
```

**Timestamp format:** `audio_start` and `video_start` use MM:SS strings (e.g. `"01:15"` for 1 minute 15 seconds). `audio_duration` and clip `duration` use numbers in seconds.

**Critical constraints:**
- `audio_start` must be valid MM:SS format, non-negative
- `audio_duration` must be positive (seconds)
- Every clip must have valid MM:SS `video_start` and positive `duration` (seconds)
- Sum of all clip durations must equal `audio_duration` (within 0.5s tolerance)
- Clip order is intentional — not necessarily chronological. Non-linear ordering creates dynamic edits.

## Workflow: From Files to Final Video

### Step 1: Generate EditPlan via Gemini

Run the Gemini script to analyze video + audio and produce a plan:

```bash
# Fresh upload (default: files kept 48h for reuse, ECLIPTIC_FILES printed on stderr):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/gemini-edit-plan.sh \
  --video <video_path> \
  --audio <audio_path> \
  --prompt "<user's edit description>"

# Reuse previously uploaded files (skips upload, much faster):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/gemini-edit-plan.sh \
  --video-uri <uri> --video-mime <mime> \
  --audio-uri <uri> --audio-mime <mime> \
  --prompt "<different description>"

# One-shot mode (delete files immediately after use):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/gemini-edit-plan.sh \
  --video <video_path> \
  --audio <audio_path> \
  --prompt "<description>" --cleanup
```

- Outputs EditPlan JSON to stdout, progress to stderr
- Requires `GEMINI_API_KEY`, `curl`, and `jq`
- Gemini watches the video and listens to the audio simultaneously

**Supported formats** (the Interactions API enforces these — anything else is rejected):

- Video: mp4, mov, avi, mpeg, mpg, webm, wmv, 3gpp (not mkv — see Troubleshooting)
- Audio: mp3, wav, aac, ogg, flac, m4a, opus, aiff

**File lifecycle.** The script keeps uploaded files by default so subsequent runs can reuse them without re-uploading. Gemini enforces a 48-hour TTL — after that, URIs go stale and must be re-uploaded. Each run emits an `ECLIPTIC_FILES` JSON line on stderr containing `video_name`, `audio_name`, URIs, and MIME types — capture this to iterate with `--video-uri` / `--audio-uri`. The script also prints the exact `cleanup-gemini-files.sh` command at the end of every fresh-upload run so deletion is explicit and copy-pasteable. If the `ECLIPTIC_FILES` line is lost, `bash ${CLAUDE_PLUGIN_ROOT}/scripts/list-gemini-files.sh` lists everything currently uploaded — names, URIs, MIME types, and expiration times. To flip the default to one-shot deletion, pass `--cleanup` or export `GEMINI_CLEANUP=1` in the environment. `--no-cleanup` is accepted as a no-op alias for the default.

**Model selection.** The s