beat-sync-video-editing

Original：🇺🇸 English
Translated

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.

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Sourceecliptic-ai/skills
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NPX Install

npx skill4agent add ecliptic-ai/skills beat-sync-video-editing

Tags

Translated version includes tags in frontmatter
beat-sync-editingffmpeg-filteredit-plan-workflowgemini-integrationvideo-editing-automation

SKILL.md Content

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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 (files auto-deleted after):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/gemini-edit-plan.sh \
  --video <video_path> \
  --audio <audio_path> \
  --prompt "<user's edit description>"

# Keep files for reuse (outputs ECLIPTIC_FILES JSON to stderr):
bash ${CLAUDE_PLUGIN_ROOT}/scripts/gemini-edit-plan.sh \
  --video <video_path> \
  --audio <audio_path> \
  --prompt "<description>" --no-cleanup

# 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>"
  • 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
  • Use 
    --no-cleanup
    + reuse mode for fast iteration with different prompts

Step 2: Validate the Plan

bash
echo '<plan_json>' | bash ${CLAUDE_PLUGIN_ROOT}/scripts/validate-plan.sh
  • Outputs 
    {"valid": true, "errors": []}
    or 
    {"valid": false, "errors": [...]}
  • Exit code 0 = valid, 1 = invalid

Step 3: Build FFmpeg Filters

bash
echo '<plan_json>' | bash ${CLAUDE_PLUGIN_ROOT}/scripts/build-filter.sh
  • Outputs 
    {"videoFilter": "...", "audioFilter": "...", "fullFilter": "..."}
  • The 
    fullFilter
    field is what goes into FFmpeg's 
    -filter_complex
    argument

Step 4: Render with FFmpeg

bash
ffmpeg -y -i "<video_path>" -i "<audio_path>" \
  -filter_complex "<fullFilter>" \
  -map "[outv]" -map "[outa]" \
  -c:v libx264 -preset fast -crf 23 \
  -c:a aac -shortest \
  "<output_path>"

FFmpeg Filter Anatomy

For a 3-clip edit, the 
fullFilter
looks like:
[0:v]trim=start=8.000:duration=2.000,setpts=PTS-STARTPTS[v0];
[0:v]trim=start=45.000:duration=1.500,setpts=PTS-STARTPTS[v1];
[0:v]trim=start=22.000:duration=3.000,setpts=PTS-STARTPTS[v2];
[v0][v1][v2]concat=n=3:v=1:a=0[outv];
[1:a]atrim=start=13.000:duration=6.500,asetpts=PTS-STARTPTS[outa]
  • [0:v]
    = first input (video), 
    [1:a]
    = second input (audio)
  • trim
    extracts a segment, 
    setpts=PTS-STARTPTS
    resets timestamps
  • concat
    joins all video segments in order
  • atrim
    extracts the audio section
For the full FFmpeg filter reference, see 
references/ffmpeg-filters.md
.

Troubleshooting

Duration mismatch error: Clip durations don't sum to 
audio_duration
. Fix by adjusting the last clip's duration to absorb the difference, or re-run Gemini with a stricter prompt.
FFmpeg "Error" in stderr: FFmpeg writes progress and warnings to stderr. Only treat it as a real error if the output file wasn't created. Check for actual error patterns like 
No such file
, 
Invalid data
, or 
Conversion failed
.
Gemini returns poor clips: Add specificity to the prompt. Instead of "make an edit", say "make a fast 30-second action edit, cut every 1-2 seconds on the beat drops, start from the chorus".

Additional Resources

Reference Files

  • references/ffmpeg-filters.md
     — Detailed FFmpeg filter_complex syntax, encoding options, common flags
  • references/edit-plan-schema.md
     — Full EditPlan JSON schema, validation rules, edge cases

Scripts

  • ${CLAUDE_PLUGIN_ROOT}/scripts/gemini-edit-plan.sh
     — Upload to Gemini via REST API, get EditPlan (supports 
    --no-cleanup
    and file reuse)
  • ${CLAUDE_PLUGIN_ROOT}/scripts/validate-plan.sh
     — Validate EditPlan JSON
  • ${CLAUDE_PLUGIN_ROOT}/scripts/build-filter.sh
     — Convert EditPlan to FFmpeg filters
  • ${CLAUDE_PLUGIN_ROOT}/scripts/cleanup-gemini-files.sh
     — Delete uploaded files from Gemini when done iterating