First still: the line overflowed the frame on both sides — 118px type plus flex gaps is wider than 1280px, and the overflow clips silently. Reduced to 92px and re-shot the still: still clipped.
Second fix took the type to 80px with tighter gaps; the settled frame now holds the full line with margins on both sides. The lesson is written into the prompt's gotchas: measure the line before you animate it.
Original promptTested
Remotion kinetic typography prompt — beat-synced type
Banned list ✓Beat grid ✓Build method ✓Self-review ✓
<direction>
An 8-second kinetic typography film in Remotion for the line "TYPE THAT MOVES ON BEAT.". Words spring in one per beat at 120 BPM, the last word in the accent colour. A row of beat ticks runs across the top of the frame and lights up as the beats pass — the grid is part of the picture, so the sync is verifiable. Near-black background, white type, one orange accent.
Banned: glows, gradients, particle bursts, bouncy cartoon easing, words that drift or float after landing.
</direction>
<structure>
16 ticks = 16 beats at 15 frames per beat (120 BPM, 30fps). Beat 1: first word springs up from below with a small overshoot. Each following beat: the next word lands; downbeat ticks (every 4th) light in accent. After the last word: an accent rule draws under the line and the caption "120 BPM — EVERY WORD ON THE GRID" fades in. Hold.
</structure>
<build>
One Remotion composition, 1280x720 landscape, 30fps. Word entrances are spring() (damping 13, stiffness 210) started at frame 10 + i × beatsPerWord × 15. Tick fill is a pure function of floor(frame / 15). Fit rule: measure the full line at the chosen size BEFORE animating — if it exceeds the frame, reduce the size; never let flex overflow clip the first or last word.
</build>
<gotchas>
Liberation/Arial bold is wider than it looks in a design tool: this line needed 80px, not the 118px that 'felt' right, and two stills caught the clipping. Check the settled frame at full width, not a thumbnail.
</gotchas>
Before you finish: step through the timeline at five points and fix anything that overlaps, clips the frame, or drifts off the beat grid.