/render-3d-character-explainer

name: render-3d-character-explainer
description: Assemble a glossy 3D-character animated-explainer video ad (~77s, 9:16) built on an "N types of X" listicle spine — a recurring human protagonist plus a locked cast of N persona characters, one per list item. Given the per-scene i2v clips + a per-scene target-duration table + a narration track, it trims each clip to its scene window, re-encodes every segment to identical 1080x1920/30fps/libx264/yuv420p (decrease+pad, never crop) so the concat demuxer never drops frames, concats, and muxes audio — in RESTYLE mode the source ad's VO+music mix is reused verbatim, in ORIGINAL mode fresh per-scene VO (loudnorm I=-14) is mixed under an optional music bed (loudnorm I=-26). A static-still fallback loops a scene's keyframe when its clip is missing/failed, so the master always assembles; libass captions are burned last. FREE deterministic assembly (Python + ffmpeg, no bash, no paid calls); the recipe supplies the clips, keyframes, VO or source audio, and caption table and gates the paid cast-anchor/keyframe/Kling-i2v/VO/music calls to their own capabilities. Use for the 3d-character-explainer listicle format.
status: active

render-3d-character-explainer

The free, deterministic renderer for the **3d-character-explainer** video ad format — the glossy Pixar-style 3D spot built on an **"N types of X" listicle** spine, where a recurring human protagonist plus a locked cast of **N persona characters (one per list item)** carry a hook → "deeper story" → cast-reveal → one beat per list item → kicker → product test → relieved payoff. This capability is the **FREE assembly stage only**. All generative work (Nano-Banana cast anchors + per-scene keyframes, Kling-V3 i2v clips, ElevenLabs VO + music, or a source ad's audio reused verbatim) happens upstream in the recipe and is handed to this capability as files.

It ports the validated compose recipe from the Bristle "Six Types" restyle run (`_render_full.sh` — per-scene trim → normalize 1080×1920/fps30 → concat -c copy → mux the source audio, with a static-still fallback on any failed clip). The assembly is deterministic — iterate the cut for free, re-roll only the offending paid beat.

Two modes

• **Restyle mode** (`audio_mode: "restyle"`, the reference run) — re-tell a finished source

ad, beat for beat, as 3D character comedy. The source ad's **audio mix (VO + music bed) is reused VERBATIM** (`source_audio`), and the per-scene `target_sec` table is inherited from the source's scene timing. No new VO or music is rendered. The trims must sum to the source audio length.

• **Original mode** (`audio_mode: "original"`) — the ad authors its own narration. Each scene

carries a measured VO cue (`scenes[].vo`, `target_sec` = the ffprobe'd VO duration) which is concatenated into a VO track (loudnorm I=-14) and optionally mixed under a `music_bed` (loudnorm I=-26 then `volume`, `amix normalize=0`).

What it does (the deterministic recipe)

1. **Per-scene retime.** Each i2v clip is trimmed to its scene `target_sec` and normalized to identical dims/fps/SAR (`scale=W:H:force_original_aspect_ratio=decrease,pad=W:H:(ow-iw)/2:(oh-ih)/2:color=<pad>,fps=30,setsar=1`). A clip **shorter** than its window is extended with `tpad=stop_mode=clone`; a longer one is `-t` trimmed. Decrease+pad (never crop) preserves the full 9:16 keyframe framing. 2. **Static-still fallback.** For any scene whose `clip` is missing or failed to render, the scene's `keyframe` PNG is looped (`-loop 1`) for `target_sec`, so the master always assembles. Fallback scenes are printed at the end. 3. **Identical re-encode + concat.** Every segment is re-encoded `libx264 -crf 18 -pix_fmt yuv420p -r 30` even if already correct — a dims/framerate mismatch makes the concat demuxer silently drop frames — then concatenated via the concat demuxer (`-c copy`). 4. **Audio.** Restyle: `source_audio` muxed verbatim (`-map 0:v -map 1:a`), clamped to the video length. Original: per-scene VO track (optional `atempo`, `apad`, `-t` clamp) → loudnorm → optionally mixed under the music bed. 5. **Captions last.** `make_captions.py` emits a libass `.ass` (one cue per scene, `start = scene_start + 0.08s`, suppressed on any scene with no caption — e.g. a product/end-card beat carrying its own typeset copy). `compose.py` burns it as the final filter so captions sit on top. Word-level energy-pop captions (Whisper on the narration) are the recipe's upstream option — produce that `.ass` externally and point `captions_ass` at it; compose burns whatever `.ass` it's handed.

Scripts (free — Python + ffmpeg, no bash, no paid calls)

• `scripts/make_captions.py` — emits the per-scene libass `.ass` from the SAME scene table

compose reads, so caption windows stay in lockstep with the cut. Run before `compose.py` (or leave `captions_ass` unset / pointing at nothing to skip captions).

• `scripts/compose.py` — the assembler: per-scene trim + identical 1080×1920/30fps re-encode

(static-still fallback on missing clips) → concat → audio (restyle verbatim / original mix) → burn captions → master mp4.

• `scripts/config.example.json` — the shape of the `config` the recipe binds (the

brand-neutralised "Six Types" restyle values as a worked reference).

Inputs (all via `--config` + a runtime work dir — NO hardcoded paths)

`config.json` carries: `audio_mode` (`restyle` | `original`), `scenes[]` (each `{id, clip, keyframe, target_sec, caption?, vo?, atempo?}` where `target_sec` is the source-inherited window in restyle mode or the **measured** VO window in original mode, and `keyframe` is the static-still fallback source), `source_audio` (restyle), `music_bed` + `music_volume` + `atempo` (original), `width`/`height` (default 1080×1920), `pad_color` (letterbox colour), `captions_ass`, and `caption_style`. See `config.example.json`.

Craft rules (load-bearing — faithful to the source molecule + reference run)

• **R