Game Trailer from Code (Steam trailer and store images)
/game-trailer-from-code
A GameSkill original: turn your own running game into a 15-second Steam gameplay trailer and every store image with code. Frame-exact capture, a JSON cut list, zh/en captions and SRT, a soundtrack synced to game events, an H.264/AAC encode, and a checker for Steam's trailer rules, loudness, the 6-second microtrailer and the capsule sizes.
- License
- MIT
- By
- By GameSkill
Tested by GameSkill
35/35 checks passed on Node 20 + Chrome 156 headless + ffmpeg 7.1 (libx264, AAC) (2026-10-28): trigger, a runnable example, a screenshot and self-check, one job per skill, and English + Chinese docs. Trigger checks match prompts against skill descriptions; they are not a live agent run.
Test reportGameSkill's tested copy
Written and tested by GameSkill for gameskill.dev. The ZIP holds the whole skill: SKILL.md and its Chinese version, scripts, a runnable example, tests, the self-check list and our test report.
A GameSkill original, released under MIT. The ZIP keeps LICENSE and CREDITS.md, which lists the workflow inspiration, the CC0 test assets and the third-party libraries with their licenses.
Self-check
- 只用了用户自己游戏的画面和合成音效 / Only the user's own game footage and synthesised sound
- 第一帧就是实机画面，每段镜头 1.2 到 4 秒，结尾卡不超过 2 秒 / Gameplay in the first frame, shots 1.2-4 s, end card at most 2 s
- check-trailer 对中英两个版本都是 PASS / check-trailer says PASS for both the en and zh versions
- capsule 和截图里除了游戏名没有其他文字 / No text but the title on capsules and screenshots
- 静音看过一遍，手机尺寸看过一遍 / Watched once muted and once at phone size
- 画面里有 AI 生成的素材就在内容调查问卷里写明 / AI-made assets on screen are listed in the Content Survey
- npm test 和 npm run test:browser 都通过 / npm test and npm run test:browser pass
Install
Tell your AI
Install the skill from https://gameskill.dev/skills/game-trailer-from-code/install.md
GameSkill's tested copy
mkdir -p .claude/skills
curl -fsSL https://gameskill.dev/dl/skills/game-trailer-from-code.zip -o /tmp/gameskill-game-trailer-from-code.zip
unzip -oq /tmp/gameskill-game-trailer-from-code.zip -d .claude/skills
rm /tmp/gameskill-game-trailer-from-code.zipWhat you get
- tools/capture.mjs: a virtual clock for frame-exact, repeatable capture of a browser game
- tools/make-trailer.mjs: cut list to trailer_en.mp4 and trailer_zh.mp4, SRT files, 5 screenshots, 9 capsule and library images, store GIF/WebP, contact sheet
- tools/check-trailer.mjs: PASS/FAIL against Steam's trailer and store-asset rules, loudness, true peak, microtrailer seconds, black and frozen stretches
- src/sound.js: a synthesised music bed and cues on game events, no audio files
- Lantern Moth example and 10 Node tests plus 11 end-to-end checks
Good fit
- Indie and web games that need a first Steam trailer and store images
- Fixing trailer uploads Steam rejects or re-times (size, fps, bitrate, sample rate)
- Rebuilding the trailer after every content update with the same cut list
Not for
- Cinematic, story or live-action trailers that need an editor and a director
- Launch timing, refunds, reviews and sales retros: see steam-launch-check
Try this prompt
Make a 15-second Steam gameplay trailer and the store capsules for my browser game, with Chinese and English captions.About this skill
A GameSkill original. Your own running game plus a JSON cut list becomes a Steam-ready 15-second gameplay trailer in two languages and the full set of store images, and a checker says PASS or FAIL against Steam's published rules.
Agent steps
- Only the user's own game: no other games' footage, music, logos or characters.
- Deterministic capture:
tools/capture.mjsswaps in a virtual clock (performance.now,Date.now,requestAnimationFrame,Math.random), so every build gives the same frames. - Cut list: 6 shots of 1.2-4 s, gameplay in the first frame, captions in en and zh, end card at most 2 s.
- Build: captions, card and capsules are HTML rendered to transparent PNGs; key art is re-captured without the HUD.
- Sound: a synthesised bed plus cues on game events, normalised to -14 LUFS with true-peak headroom for AAC.
- Check until PASS: Steam spec, loudness, every 1-second microtrailer window, black and frozen stretches, SRT timings, capsule and screenshot sizes.
- List AI-made assets that appear on screen in Steam's Content Survey, with the rest of the game's AI use.
Common errors it fixes
- Uploads at 1024x576, 25 fps or 22 kHz that Steam fails to process.
- Logo or black openings that turn into blank seconds in the microtrailer.
- Text or HUD numbers on capsules, and AAC encodes that push the true peak over -1 dBTP.
Credits
QA ideas (black and frozen frames, loudness, the first seconds) and staged checks from video-director by win4r (MIT). No code or text was copied; capture, cut list, checks, sound and text are ours. Steam rules from the Steamworks documentation, checked 2026-10-28.
Requirements
- Node.js 20+, Google Chrome and ffmpeg/ffprobe (libx264, AAC)
- A game with a demo or autopilot mode (browser games directly; native engines via a fixed-step replay)
Topics
FAQ
Based on video-director by win4r (MIT). Ideas only: GameSkill wrote the code and text; CREDITS.md in the ZIP lists every source.
Works well with
Skills the author points to as related or as the better fit for neighbouring tasks.
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