Countdown Video

Make a countdown that ends exactly when it should. The whole craft is one idea: derive the remaining time from the frame (or a monotonic timestamp), then format and animate that number — never count down with a setInterval. Covers livestream "starting soon" screens, launch/sale countdowns, and looping backgrounds.

When to use

• "Starting soon" / "be right back" livestream screens with a 5–10 min timer.
• Launch and flash-sale countdowns (dd:hh:mm:ss down to a target date; mm:ss for urgency).
• Any animated counter where the number must land on zero on the exact frame.

The one rule: drive the number from the clock, never a tick

A setInterval(fn, 1000) countdown drifts — the callback fires at least 1000 ms later, never exactly, and stacks up when the tab is throttled or a render frame is slow. Reports of ~1 second lost per minute are common. The fix is the same for rendered video and live web: compute remaining time as a pure function of an authoritative clock, so a late frame self-corrects on the next frame instead of accumulating error.

Never store remaining time in state and decrement it. Recompute it every frame.

Frame-accurate countdown (Remotion → MP4)

useCurrentFrame() is deterministic: frame N is always rendered at exactly N/fps seconds. Subtract from the total and the timer is drift-free by construction.

import { useCurrentFrame, useVideoConfig } from "remotion";

export const Countdown: React.FC<{ durationInSeconds: number }> = ({
  durationInSeconds,
}) => {
  const frame = useCurrentFrame();
  const { fps } = useVideoConfig();

  // remaining seconds, clamped at 0 — ceil so "1" shows for its full second
  const elapsed = frame / fps;
  const remaining = Math.max(0, Math.ceil(durationInSeconds - elapsed));

  return <div style={{ fontVariantNumeric: "tabular-nums" }}>{formatMMSS(remaining)}</div>;
};

durationInSeconds is a prop, not a constant — the same composition renders a 5-minute stream timer or a 30-second sale timer by changing one input. Set the composition's durationInFrames to durationInSeconds * fps so the video is exactly as long as the countdown.

Web timer (live page, requestAnimationFrame)

For a live page, drive an rAF loop from performance.now() and only repaint when the displayed second changes (no work 60×/sec for a 1 Hz number):

const start = performance.now();
let lastShown = -1;
function tick(now) {
  const remaining = Math.max(0, Math.ceil(duration - (now - start) / 1000));
  if (remaining !== lastShown) { render(remaining); lastShown = remaining; }
  if (remaining > 0) requestAnimationFrame(tick);
}
requestAnimationFrame(tick);

Counting down to a fixed date is the same idea with Date.now(): Math.max(0, target - Date.now()). See references/countdown-cookbook.md for the full date-target version with timezone handling.

Time formatting

Break a remaining-seconds integer into fields with division + modulo, then zero-pad. Pick the format to fit the duration — never show 00d 00h 05m when minutes is all that matters.

const pad = (n) => String(n).padStart(2, "0");
const formatMMSS = (s) => `${pad(Math.floor(s / 60))}:${pad(s % 60)}`;
const formatDHMS = (s) => {
  const d = Math.floor(s / 86400), h = Math.floor((s % 86400) / 3600);
  const m = Math.floor((s % 3600) / 60), sec = s % 60;
  return `${pad(d)}:${pad(h)}:${pad(m)}:${pad(sec)}`;
};

Always set font-variant-numeric: tabular-nums (or a monospace digit font) so digits keep equal width and the layout does not jitter as numbers change.

Digit roll / flip transitions

A flat number swap reads as cheap; the rolling "odometer" look sells the countdown. Render each digit as a vertical strip 0–9 and translate it by -digit × digitHeight. Animate the position, not the text content, so the change is a glide, not a pop.

.reel { height: 1em; overflow: hidden; }
.reel .col { transition: transform .45s cubic-bezier(.22,1,.36,1); }
/* col holds stacked 0..9; shift by -value em */

In Remotion, drive the strip offset off the frame instead of a CSS transition (so it is deterministic). The flip-card style (top half folds down over the bottom) and the per-digit reel are both detailed, with runnable components, in references/digit-flip.md.

Looping background

Stream screens hold for minutes, so the background must loop seamlessly. Build motion on a cycle that divides evenly into the timeline (e.g. a gradient or particle drift whose period is loopFrames), and read it as frame % loopFrames so there is no visible seam at the wrap. Keep it low-contrast and slow — the number is the subject; the background is ambience. Recipes in references/countdown-cookbook.md.

Output checklist

• Remaining time recomputed from useCurrentFrame() / performance.now() every frame — no setInterval decrement.
• Timer hits 00:00 on the exact intended frame; durationInFrames === durationInSeconds × fps.
• Duration is an input prop, not a hardcoded constant.
• Digits use tabular-nums; layout does not shift as numbers change.
• Format matches the span (mm:ss vs dd:hh:mm:ss); leading zero units dropped when distracting.
• Background loop period divides the timeline evenly; no seam at the wrap.

Deliver & verify (rendered stills → MP4)

Packaged helper (scripts/): tile your stills with scripts/contact-sheet.sh sheet.png f-hook.png f-mid.png f-end.png, then assert the encode with scripts/probe-mp4.sh out.mp4 [WxH] [fps]. See scripts/README.md.

The countdown ships as a Remotion composition (<Composition> + zod schema + defaultProps, durationInSeconds a prop) — the timer is a pure function of useCurrentFrame(), never setInterval / Date.now() / Math.random(). Set durationInFrames = durationInSeconds * fps. Deliverable = out/*.mp4 + the project. 9:16 vertical (1080×1920) is the default.

Verify loop — render stills → inspect → encode. The whole point is frame-accuracy, so check the digit value at exact frames before encoding.

# Stills at start / mid / end — WITH SHIPPED PROPS (the real duration you'll render)
npx remotion still Countdown out/f-start.png --frame=0   --props='{"durationInSeconds":300}'
npx remotion still Countdown out/f-mid.png   --frame=N   --props='{"durationInSeconds":300}'
npx remotion still Countdown out/f-end.png   --frame=L   --props='{"durationInSeconds":300}'  # L = durationInFrames-1

# Inspect each PNG — the digits must read EXACTLY the frame/fps math:
#  - at frame N, displayed = ceil(durationInSeconds - N/fps)  (e.g. 300s @ 30fps, frame 4500 → 150s → "02:30")
#  - last frame reads 00:00 (or the end-state hold); no drift, no off-by-one second
#  - tabular-nums: layout does not jitter between frames
#  - 9:16 safe area: the timer + brand block sit clear of top ~12% and bottom ~20-35% UI and the right action rail

npx remotion render Countdown out/countdown.mp4 --props='{"durationInSeconds":300}'   # encode once digits verify
npx remotion render Countdown out/demo.gif --codec=gif                                 # README proof clip

Use npx remotion compositions to confirm durationInFrames/fps, then compute the frame for any second you want to check.

Before you finish:

1. Stills render cleanly at frame 0, mid, and last — no errors.
2. The digit value at frame N equals ceil(durationInSeconds - N/fps) exactly; last frame hits 00:00 on the intended frame (no drift / off-by-one).
3. Timer + brand stay inside the 9:16 safe area at every checked frame.
4. Frame-driven only — no setInterval / Date.now() / timers; tabular-nums so layout holds.
5. Shipped durationInSeconds (not just defaultProps) renders correctly; MP4 encoded, GIF optional.

Reference files

• references/countdown-cookbook.md — complete runnable Remotion <Countdown> (configurable duration, mm:ss / dd:hh:mm:ss, end-state hold), the count-down-to-a-fixed-date web component with timezone handling, a "starting soon" stream-screen layout (brand block + social handles + looping gradient background), and the seamless-loop background pattern.
• references/digit-flip.md — two deterministic digit-animation components: the odometer reel (vertical 0–9 strip driven by frame) and the flip-card (top-half fold) effect, plus when each suits launch vs sale vs stream.