Zach D Films skill

/zach-d-films

┌──────────────────────┐
│      blue sky        │  procedural 3D people and props, soft shadows
│    ◕‿◕   ⛨           │  depth of field, bloom, light grain
│   /▓▓▓\  ⟶  •        │  slow-motion impacts, sparks, a red force ripple
│     ▓▓               │
│     arrows           │  1-3 word captions, white bold, lower third
└──────────────────────┘

A worked example comes with it: engine/ is a finished 29.5 s short, "Could ancient armour stop a bullet?" (9 shots: a gun shot, a slow-motion bullet flattening on a vest, a sword on chain mail, a mace on plate with a red ripple, an archer, an arrow and a scream, a bullet through two stands). It ships without its voiceover, so you bring a voice. Not affiliated with Zack D. Films; "the style" means the format: a question, a misconception, a "But" twist, building examples and a payoff.

First use

This skill's folder is the "Base directory" Claude Code shows when it loads it.

SKILL_DIR="<base directory of this skill>"
KIT=$(python3 -c 'import os,sys;print(os.path.realpath(os.path.join(sys.argv[1],"..","..","kit")))' "$SKILL_DIR")
[ -d "$KIT/node_modules/playwright" ] || bash "$KIT/setup.sh"
[ -x "$KIT/.venv/bin/python" ] && [ -d "$KIT/models" ] || bash "$KIT/setup.sh" --voice   # word timings + free voice, ~1 GB once
PY="$KIT/.venv/bin/python"

Needs ffmpeg, Node and Python 3.9+. It renders with WebGL in headless Chrome: about 0.2 to 0.5 s a frame on a Mac, a few minutes for a short. On a machine without a usable GPU, set GL=swiftshader (much slower).

The engine

File	What
src/shots.js	The edit. CAPTIONS ([start, text, end?]), FADES (dips to black), DURATION, one function per shot and the SHOTS list ({start, end, build}). A shot's build({makeStage}) returns {scene, camera, update(t)}; update gets time inside the shot and may return {dof, bloom, exposure}.
src/human.js	makeHuman(outfit): a poseable cartoon person ('vest', 'chainmail', 'plate', 'knight', 'archer'). setPose({joint: [x, y, z]}) for pelvis spine chest neck head lSh lEl lWr rSh rEl rWr lHip lKn lAn rHip rKn rAn (+ drop), setMouth(0..1), lerpPose(a, b, t), standArmor(kind).
src/props.js	pistol, gunArm, bullet (with a flatten morph), sword, shield, mace, arrow, bow, stand, glowSprite, sparks, streak, rippleOverlay (the red force ripple).
src/anim.js	kf keyframes, easings, range, cam(fov), place(camera, pos, look), shake, ikArm (2-bone arm IK so hands can grab things).
src/textures.js, src/materials.js	Canvas-made steel scratches, chain-mail rings, wood, fabric, skin, and the materials built on them.
src/main.js	Renderer, sky, lighting, depth of field, bloom, grade, and window.renderAt(t).

Steps

1. Script. Use the user's script, or draft one in the format: "If you…" hook, "some people think…", a "But" twist, examples that build, the mechanism, a payoff that answers the hook. About 2.5 words a second (70 to 90 words for 30 s). Check the facts.
2. Project. Copy the engine to a new folder (<project> must not exist yet) and link the shared packages:

   cp -R "$SKILL_DIR/engine" <project> && ln -s "$KIT/node_modules" <project>/node_modules
   

   Write the script into <project>/script.json as a list of sentences.
3. Voice. Best is the user's own recording; convert it with ffmpeg -i <take> -ac 1 -ar 44100 <project>/audio/vo.wav. Otherwise, from the project, the free Kokoro voice: "$PY" "$SKILL_DIR/../stick-figure/engine/tools/tts_kokoro.py" [voice] [speed] (defaults am_michael 1.12; also af_heart, am_adam, bm_george) writes audio/vo_kokoro.wav; copy it to audio/vo.wav. For the browser preview only, also save it as audio.m4a (main.js plays that file).
4. Captions. "$PY" "$KIT/words.py" audio/vo.wav script.json writes audio/vo.words.json (the voiceover's name with .words.json). Then python3 captions.py audio/vo.words.json prints CAPTIONS and DURATION to paste over the ones in src/shots.js. Set FADES around your "But" cut (the example dips at 6.2 s), or [].
5. Shots. Plan a shot every 2 to 4 s (8 to 10 for 30 s, 3 for 10 s), cutting on caption beats, the mechanism shot longest. Write one function per shot by copying the closest example, change the props, poses and camera, and list them in SHOTS with start and end times (delete the example functions you don't use).
   • update(t) must depend only on t: a render can start in the middle of a shot. Example shot 7 keeps state between frames and needs a workaround, so don't copy that pattern.
   • Useful helpers inside shots.js: standPose, STAND, handsOnHips, surfaceHit (where a projectile meets a mesh). In props.js: box, shadow. rippleOverlay needs one mesh to sit on; for a target made of parts, give it an invisible disc (with shadows off).
   • New props go in props.js as small functions that return a THREE.Group. sparks are glowing points, so splinters or dust need their own meshes.
   • At 9:16 the frame is narrow (about 19° wide at fov 34). To keep a projectile in frame, ride behind it.
   • Keep faces and key props out of the caption band (y about 950 to 1030 of 1280) and away from the frame edges.
6. Stills. From the project: node render.mjs stills 1.5,6.8,14 stills. Look at every shot before a full render.
7. Render. node render.mjs video silent.mp4 30 (about 0.2 to 0.5 s a frame), then add the voice, level it and scale to 1080x1920:

   ffmpeg -i silent.mp4 -i audio/vo.wav -map 0:v -map 1:a -vf scale=1080:1920:flags=lanczos -c:v libx264 -crf 17 -pix_fmt yuv420p -af "apad,loudnorm=I=-14:TP=-1.5" -c:a aac -b:a 192k -shortest <name>.mp4
   

8. Hand over the mp4 path.

For a live preview, serve the project (python3 -m http.server 8000) and open index.html (click to play with audio.m4a), or index.html?t=14.5 for one frame.

Style

• Bright blue studio sky, soft daylight, metal that reads as metal. Cartoon people are simple shapes with big expressive faces; keep them in proportion with the props.
• Slow motion on the impact, a short camera shake, sparks, bloom on hot things. The red ripple shows force spreading.
• Quick cuts on caption beats; one dip to black on the "But" turn. Captions are white, bold, 1 to 3 words.