/video-thumbnail-generator

name: video-thumbnail-generator
description: Create platform-ready thumbnails from real video frames. Use when the user wants a thumbnail, cover image, YouTube cover, Shorts cover, Bilibili cover, Xiaohongshu cover, or other video poster image.

Video Thumbnail Generator

Use this skill to create a high-clarity thumbnail or cover image from the actual video content.

Non-Negotiables

1. Use the real video as visual evidence.

• If the thumbnail shows a person, product, UI, frame, or scene from the video, extract or inspect real frames.
• Never invent a generic software interface, fake product screen, or unrelated person.

2. Read style references before recommending styles.

• Use `references/thumbnail-styles.md` and `references/thumbnail-style-recipes.md`.
• Only offer style directions supported by those references or by the user's explicit instruction.

3. Keep text short and readable.

• Usually 2-5 words.
• Avoid thin type, low contrast, small labels, and clutter.

Workflow

1. Confirm platform and aspect ratio if missing.

• YouTube / Bilibili: usually 16:9.
• Shorts / TikTok / Douyin: usually 9:16.
• Xiaohongshu / WeChat Channels: usually 3:4.
• Correct ambiguous ratio language gently, especially 4:3 vs 3:4.

2. Read project state, transcript, and available media context. 3. Inspect candidate frames:

• expressive face
• product or UI clearly visible
• dramatic action moment
• clean composition
• strong lighting or clear subject separation

4. Classify the thumbnail job:

• talking-head / opinion / tutorial
• product / software / demo
• cinematic / documentary / art
• entertainment / challenge / reaction
• education / business / concept

5. Propose concise title text options. 6. Offer 3-6 clearly different style directions.

• Each option should name the composition, not only a channel/style label.
• Exclude weak options.
• Wait for user choice when the direction is not obvious.

7. Generate thumbnail options using selected real frames and the selected style. 8. Check mobile readability, subject fidelity, product/UI truthfulness, and visual contrast. 9. Present results and offer targeted adjustments.

Prompt Shape

[Platform] thumbnail, [aspect ratio / dimensions], [style name].

COMPOSITION: [subject position, scale, background, graphic balance]
REAL REFERENCE: [describe selected frame zone by zone]
TEXT: "[short title]" in [high-contrast style]
STYLE: [one-line style recipe from references]
CONSTRAINTS: readable at mobile size, no fake UI, no watermark, no play button.

References

• `references/thumbnail-styles.md`: style library from real thumbnail analysis.
• `references/thumbnail-style-recipes.md`: quick style recipes and prompt patterns.
• `references/field-testing-notes.md`: known failure modes.