Onboarding bento demo videos

The first onboarding step (WelcomeScreen) shows a bento grid of feature cards. A card with a media entry plays a short, muted, looping screen recording; cards without one show a static placeholder. The featured (large, top-left) card is the only one that plays at a time — hover just moves the highlight.

Thing	Where
Clips + posters	packages/ui/src/features/onboarding/assets/<feature>-<light|dark>.{mp4,jpg}
Wiring (MEDIA map, startTime)	packages/ui/src/features/onboarding/components/WelcomeScreen.tsx
<video> element + play/seek logic	packages/ui/src/features/onboarding/components/FeatureBentoCard.tsx
Optimizer script	scripts/optimize-onboarding-videos.mjs (pnpm optimize:onboarding-videos)

Why clips need optimizing (the "it feels laggy" fix)

Raw screen recordings hitch in this UI for two reasons, both fixed by re-encoding:

1. moov atom at the end of the file. Without faststart the player must read to EOF before it can start, so first-play and every seek stutter. We seek on mount and on every loop (FeatureBentoCard parks the clip on videoStartTime), so this bites constantly. Fix: -movflags +faststart.
2. Resolution far larger than it renders. The featured slot is never wider than ~500 CSS px (the grid is max-w-[760px]). Even at 2× retina that's ~1000px, but recordings come in at ~1876px. Decoding huge frames and downscaling them — on every play and during the framer-motion slot reflow — is wasted work. Fix: cap width at 1000px (which also matches the poster width exactly).

Bitrate/size are usually already modest; decode cost and startup are the lag, not bytes. Don't chase file size at the expense of width/faststart.

Canonical encode target

H.264 · yuv420p · ≤1000px wide (keep aspect, even height) · CRF 23 · +faststart · no audio. These live as constants at the top of scripts/optimize-onboarding-videos.mjs — change them there, not ad-hoc.

Optimize existing clips

pnpm optimize:onboarding-videos          # encode any clip not already optimized
pnpm optimize:onboarding-videos --dry-run   # show what would change
pnpm optimize:onboarding-videos --force     # re-encode all (after changing the target constants)

Requires ffmpeg (brew install ffmpeg). The script tags each output with a comment marker, so re-runs skip already-optimized files — it's safe to run any time, including right after dropping in a new clip. It rewrites files in place; review the git diff --stat and the printed before/after sizes.

Add or replace a clip

1. Record light + dark variants at ≥1000px wide. The optimizer downscales to 1000px but never upscales, so anything narrower ships soft — resolution is the one thing it can't fix for you. Keep it short (~10–13s); it loops.

2. Name + drop the files as assets/<feature>-light.mp4 and assets/<feature>-dark.mp4. Two things bite every time:

   • Recordings almost always arrive with the light variant unsuffixed (foo.mp4, only foo-dark.mp4 is tagged). Rename it to foo-light.mp4.
   • The source filename (e.g. whatever's in ~/Downloads) is irrelevant — the <feature> prefix must be the media id you'll use in WelcomeScreen and follow the existing convention, not whatever the file was called.

   No assets.d.ts change needed — *.mp4/*.jpg are wildcard modules.

3. Optimize: pnpm optimize:onboarding-videos.

4. Make the poster — the still shown before play. Use the clip's first frame and leave startTime at 0, so the poster, the first played frame, and the loop point are all the same with nothing to keep in sync:

   ffmpeg -y -i assets/<feature>-<theme>.mp4 \
     -frames:v 1 -vf "scale=1000:-2:flags=lanczos" -q:v 3 \
     assets/<feature>-<theme>.jpg
   

5. Wire it up in WelcomeScreen.tsx. For a new media id, four edits, all keyed by the same slug: import the .mp4 + .jpg, add the id to the MediaId union, add its entry to the MEDIA map (startTime: 0), and set media: "<id>" on the target FeatureDef.

Replacing an existing clip

Keep the same asset filename and the wiring is untouched — none of step 5 applies. Drop the new file over assets/<feature>-<theme>.mp4, run the optimizer (a fresh drop carries no skip-marker, so it re-encodes without --force), and regenerate that poster (step 4). If you replace only one theme, re-check that light and dark still share an aspect ratio — a clip with stray padding frames differently from its sibling, and the gap shows when the user toggles theme.

Poster = first frame (and startTime = 0)

FeatureBentoCard shows the poster while a card rests, then seeks the <video> to MEDIA[id].startTime on mount and loops back there (not necessarily to 0). The simple, default contract: the poster is the clip's first frame and startTime is 0, so the still, the first played frame, and the loop point are all identical — nothing to keep in sync. Keep the poster the same pixel width as the clip (1000px) so the poster→video swap is seamless.

startTime can start/loop mid-clip if you ever need it (the code-review clip uses 3s) — but then the poster MUST be that exact frame (ffmpeg -ss <startTime> -i …), or the still jumps the instant playback starts. Prefer the first-frame default unless you have a specific reason.

Verify

# clips: moov should print BEFORE mdat, width ≤ 1000:
ffprobe -v trace <clip>.mp4 2>&1 | grep -o -m2 -E "type:'(moov|mdat)'"
ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=p=0 <clip>.mp4

# wiring: a grown MediaId union may need a formatter reflow, so let biome fix it:
npx biome check --write packages/ui/src/features/onboarding/components/WelcomeScreen.tsx
pnpm --filter @posthog/ui typecheck

To confirm playback feels smooth in the real app, use the test-electron-app skill to drive the running onboarding flow.