ever-just/agentskills

Web Embed Video Optimization

Turn a source clip (screen recording, phone export, HEVC render) into a fast, crisp, reliably-autoplaying hero/background/loop and embed it. The win is usually large: retina-aware H.264 at a sane CRF takes a 1080p screen recording from ~8 MB to ~1.5 MB with no visible loss, and fixes autoplay/codec issues.

For creating or animating video, use [[remotion]] / [[moviepy]] / [[motion-canvas]] instead — this skill optimizes footage you already have.

When to use

• Adding/replacing a hero, background, or looping demo video on a site.
• The video is too heavy, won't autoplay (mobile/Safari), errors on a codec, or looks soft.

Recipe

1. Probe first

ffprobe -v error -select_streams v:0 \
  -show_entries stream=codec_name,width,height,r_frame_rate,duration,pix_fmt,profile \
  -of default=noprint_wrappers=1 in.mp4
ffprobe -v error -select_streams a -show_entries stream=codec_name -of csv=p=0 in.mp4   # audio?
# faststart check: is 'moov' before 'mdat'? (moov at end = slow start)

2. Transcode (web-safe + retina-aware)

ffmpeg -y -i in.mp4 -vf "scale=1600:-2" \
  -c:v libx264 -profile:v high -pix_fmt yuv420p -crf 23 -preset slow \
  -movflags +faststart -an -r 30 out.mp4

• -pix_fmt yuv420p — mandatory for Safari/broad support (yuv444/422 won't play).
• -movflags +faststart — moves the moov atom to the front so it starts before fully downloaded. Without it, an autoplay hero stalls on slow links.
• -an — strip audio; a muted background loop never needs it (smaller file).
• scale=1600:-2 — encode to roughly 2× the CSS display width, not native 1080p/4K. At a ≤820px frame, 1600px is retina-crisp and much lighter. -2 keeps height even (required by H.264).
• -crf 23 -preset slow — high quality, good compression. Screen/UI content compresses especially well; bump CRF to 25–26 only if the file is still heavy.

3. Poster frame

ffmpeg -y -ss 3 -i in.mp4 -vframes 1 -vf "scale=1600:-2" -q:v 3 poster.jpg

Pick a representative moment (-ss), not a blank intro frame.

4. Embed

<video autoplay muted loop playsinline preload="auto" poster="/path/poster.jpg">
  <source src="/path/out.mp4" type="video/mp4"/>
</video>

• muted + playsinline + autoplay are all required for mobile autoplay.
• Container CSS: video{display:block;width:100%;height:auto} lets a 16:9 clip set its own height; wrap in a frame with overflow:hidden;border-radius.

5. Serve (Odoo tenants)

Store as a public ir.attachment and reference /web/content/<id> (video) and /web/image/<id> (poster) — see [[everjust-website-customization]]. Transfer the binary in via docker cp (the shell runs inside the container). Use fresh attachment IDs and repoint the view, rather than overwriting old IDs, to dodge stale browser/CDN cache. View edits need a container restart to render.

Verify (mandatory)

Confirm it actually plays with [[cdp-render-verification]] — launch Chrome with --autoplay-policy=no-user-gesture-required, then read the <video> element:

• readyState === 4 (HAVE_ENOUGH_DATA), paused === false, currentTime > 0 after a short wait (advancing), and videoWidth/videoHeight match the encode.
• Check desktop and mobile, and that the page has no horizontal overflow.

Related

• [[everjust-website-customization]] — serving via Odoo attachments + view embed.
• [[cdp-render-verification]] — the playback proof.
• [[remotion]] / [[moviepy]] — creating/animating video (the opposite job).