Stills before the render

stills is not a render. It composes each HyperFrames scene exactly as the renderer does (tokens, safe zones, word cues, the music's beat grid), opens the page in headless Chrome, seeks it to the chosen moments and tiles the frames into review/stills/stills-<quality>[-<scene>].jpg (full-size frames in review/stills/frames/). Nothing in renders/ or dist/ changes and no voice is synthesized, so it takes seconds, not minutes.

Stills and determinism

1. After spec_validate passes and before render_submit, call mcp__plugin_video-studio_engine__stills {project_dir, at: "downbeats"} when the spec has a music bed (at: "beats" for fast cuts), else {project_dir} (in/mid/out of every scene). Limit to the scenes you changed with scenes: ["s03"]; use times: [0.4, 1.2] (scene-local seconds) for exact moments.
2. Read every image in images. Each tile is labelled <scene> <moment> <time> (beat 3, bar 2, in/mid/out). Check:
   • text fits, is readable at phone size and is not cramped against an edge;
   • nothing overlaps or sits under captions or the platform UI;
   • each state change lands on its beat or bar (the label says which), and no beat shows a frame that is half-way through nothing;
   • no empty, near-identical or cluttered frames.
3. Fix the page (motion/*.html) or the spec and run stills again on the changed scenes. Render only when the sheet looks right.

Stills hand each page the same data the render does. That includes the music envelope (vs.energy, vs.bass, vs.onset) of motion pages and, with audio.beat_sync on, the beat-placed reveals of text scenes. So a still at time t matches the render's frame at t. Before the first render, reveals sit on the bed's beats at spec durations (a note says so), and the render can still move cuts.

Transitions are not in stills. Crossfades and other transitions are drawn when the scenes are assembled, and stills draw one scene at a time. After a render, use review with transitions: true to see each transition at its midpoint.

Every motion scene is also checked automatically before it renders: the page is seeked to the same times in a different order and the frames must be identical, else the scene fails with nondeterministic_scene (a clock, unseeded randomness, or state carried between frames: window.seek(t) must rebuild the whole frame from t). With props.loop, the frame at the end must match the first (loop_seam warning). The result is cached until the page changes.

Errors

• RENDER_LOCKED: a render of this project is running; wait for it (job_status), then run stills.
• Chrome or the producer missing: run doctor; the render can still fall back to ffmpeg, but stills need Chrome.
• stills at downbeats: this project has no beat grid: there is no music bed (or no clear beat); use times or count.
• A scene in skipped (footage, provider scenes, a motion page the lint refuses): fix what the reason says, or review it after the render with the review skill.