video-composer

Video Composer — orchestrated rich video production

This skill turns a request into a finished .mp4 by combining four media skills on a Remotion (React) timeline:

Layer	Skill
Images / backgrounds	nanobanana
Video clips	veo
Background music	lyria
Narration / voiceover	gemini-tts

It is an orchestrator: it does not generate media itself, it directs the skills above and assembles their output.

Workflow (must follow in order)

Step 0 — Check prerequisites & sibling skills

Run the availability check first:

python scripts/check_skills.py

All present → continue.
Some missing → this typically means another user installed video-composer standalone (e.g. via npx skills add). Prompt them to install the missing skills using the commands the script prints (from the repo README), or offer a documented fallback (see references/asset-pipeline.md → "Missing skills"). Do not silently skip a requested asset type — surface the choice.

Also confirm tooling: Node.js ≥ 18 (node -v) and npx. Remotion bundles its own ffmpeg, so ffmpeg is not required. API access for the media skills needs GEMINI_API_KEY (or Vertex AI). See references/asset-pipeline.md.

Step 1 — Gather requirements

Interview the user (use AskUserQuestion for anything ambiguous) to pin down:

Purpose / message and target audience
Duration (e.g. 15s / 30s / 60s) and orientation (16:9 / 9:16 / 1:1)
Tone / style (corporate, playful, cinematic, minimal…)
Must-haves: narration? on-screen captions? BGM mood? brand colors/logo?
Language (for narration & captions)
Any assets the user already has vs. what should be generated

Step 2 — Return a composition plan and GET APPROVAL (gate)

Produce a concise, structured plan and present it to the user. Do not generate anything or render until the user approves. The plan must include:

Overall spec: resolution, fps, total duration, orientation
A scene-by-scene table: # · duration · visual (image/video + prompt summary) · narration text · on-screen caption · transition
BGM mood and any logo/branding
Which assets are generated (and by which skill) vs fallback/user-supplied

Iterate on the plan with the user until they explicitly approve. Only then proceed.

Step 3 — Scaffold the Remotion project

python scripts/scaffold.py <project-dir>

This writes a self-contained, data-driven Remotion project (see references/remotion-template.md for the structure and the props schema). A fresh project is scaffolded per video.

Step 4 — Generate assets

Following the approved plan, call each sibling skill and place output under <project-dir>/public/{images,video,audio}/. Exact commands and timing tips are in references/asset-pipeline.md. Keep a consistent visual style across images.

BGM lives only in the lyria layer. Veo clips keep their native audio (SE, ambience, dialogue) playing on the timeline, so when generating veo clips you must always suppress embedded music — pass --negative-prompt "background music, soundtrack, musical score, BGM" and never ask for music in the prompt. Otherwise a clip's own BGM would clash with the global lyria BGM. SE/ambience are kept; only music is suppressed. Details: references/asset-pipeline.md → "Never let veo clips carry their own BGM".

Step 5 — Author the timeline (props.json)

Copy props.sample.json → props.json and fill in the scenes: reference assets by path relative to public/, set each scene's durationInFrames (round(seconds * fps)), captions, voiceover, transitions, and BGM. Schema and timing rules: references/remotion-template.md.

Step 6 — Render + multimodal self-review (autonomous loop)

python scripts/render_video.py --project <project-dir> \
  --props <project-dir>/props.json --install --review-frames 6

Then read the exported review stills with vision and score them against the rubric in references/self-review.md. Iterate autonomously — fixing the cheapest layer first (props → asset regen) — until all criteria pass or the iteration cap (default 3) is reached.

Step 7 — Deliver

When the result meets the bar, deliver the final .mp4 to the user (use SendUserFile for the artifact). If you stopped at the iteration cap with known issues, deliver the best version and list the remaining issues plus suggested next steps.

Scripts

Script	Purpose
`scripts/check_skills.py`	Detect sibling skills; print install guidance / fallbacks
`scripts/scaffold.py`	Scaffold a fresh data-driven Remotion project
`scripts/render_video.py`	`npm install` + render + export review stills

References

File	Contents
`references/asset-pipeline.md`	Exact commands to drive each media skill; timing; missing-skill handling
`references/remotion-template.md`	Project structure & the `props.json` timeline schema
`references/self-review.md`	Multimodal review rubric & the autonomous iteration loop

Props schema (quick reference)

{
  "fps": 30, "width": 1920, "height": 1080,
  "bgm": { "src": "audio/bgm.mp3", "volume": 0.22 },
  "scenes": [
    {
      "durationInFrames": 150,
      "media": { "type": "image" | "video", "src": "images/x.png", "fit": "cover" },
      "kenBurns": true,
      "captions": [ { "text": "…", "fromFrame": 0, "toFrame": 140, "position": "bottom" } ],
      "voiceover": { "src": "audio/vo1.wav", "volume": 1.0, "delayInFrames": 6 },
      "transitionToNext": { "type": "fade" | "slide" | "wipe" | "none",
                             "durationInFrames": 18, "direction": "from-right" }
    }
  ]
}

Asset src paths are relative to public/ (http(s) URLs pass through).
Total duration is computed automatically (sum of scene durations minus transition overlaps).

Principles

Approval gate is mandatory — never start generating/rendering before the user approves the plan.
Never deliver an unreviewed render — always run the self-review loop.
Prefer this repo's skills; when one is missing, prompt installation or use a documented fallback — and make the trade-off visible in the plan.
Fix cheap before expensive — edit props before regenerating assets.
One BGM bed only — music belongs to the lyria layer; always generate veo clips with music suppressed (negative prompt) so clip-embedded BGM can't clash with the global BGM. Keep the clips' SE/ambience.