Storyboard Extract

Use this when an agent needs direct visual evidence from a video rather than only sibling JSON reports.

This skill owns:

• probing video duration with ffprobe
• extracting frames with ffmpeg
• optional hybrid sampling that biases some frames toward likely scene changes and same-screen local UI updates
• writing storyboard.manifest.json
• carrying per-frame sampling reasons into the manifest when available
• giving downstream reviewers stable image artifacts to inspect

Inputs

Required:

{
  "videoPath": "./output/example-run/output.mp4"
}

Optional fields:

• outputDir: directory for frame images and storyboard.manifest.json; defaults to video-evaluator-storyboard next to the video.
• frameCount: 1 to 24, default 6.
• format: jpg or png, default jpg.
• samplingMode: uniform or hybrid, default uniform.
• changeThreshold: scene-change threshold for hybrid sampling, default 0.08.

Outputs

The skill writes frame images and storyboard.manifest.json, then returns the manifest path and manifest. Each frame records index, timestamp, image path, and sampling reason. Hybrid mode may also include detected change counts, same-screen candidate diagnostics, nearest change distance, and sampling scores.

Sequencing Guidance

Use this before storyboard-ocr. Prefer samplingMode: "uniform" for broad coverage and deterministic spot checks. Prefer samplingMode: "hybrid" when the video has sparse UI changes or you need evidence near transitions. After extraction, inspect frames directly when visual fidelity matters, then run OCR for machine-readable text.

Interpretation Notes

Sampled frames are evidence, not full coverage. change-peak frames were chosen near detected changes; coverage-fill frames preserve spread when change candidates are sparse. Hybrid diagnostics are heuristics and can miss fades, subtle animation, or very fast transitions.

Abstention Rules

Do not claim that unsampled portions of the video are correct. Abstain from text or accessibility conclusions until storyboard-ocr has run or the images have been manually inspected.

Failure Modes

The runner requires ffmpeg and ffprobe. Invalid video paths, unsupported codecs, zero-duration files, or missing binaries will fail extraction. If hybrid sampling returns no candidates, the frame plan falls back to uniform coverage.

Repo-side runner:

node --import tsx scripts/harness/storyboard-extract.ts

Installed-pack runner:

node ./.video-evaluator/agent/run-tool.mjs storyboard-extract