Make an App Preview from Screenshots (886×1920 MP4)

Two truths before you hit export

Meeting the pixel spec is not the same as clearing content review. Apple’s App Preview specifications (checked 2026-10-30) say previews are optional, up to three per device size and language, 15–30 seconds, ≤ 500MB, with iPhone’s current accepted portrait size at 886×1920—not the 1320×2868 still used for screenshots. Codecs: H.264 (.mp4 / .m4v / .mov) or ProRes 422 HQ.

Apple’s App Previews guide also expects footage of the app in use, not lifestyle shots of hands holding a phone. A screenshot slideshow can hit resolution, frame rate, and audio-track layout so you can storyboard fast. Reviewers can still ask for a real device capture if the cut feels like a marketing montage. We state that up front so “uploadable file” is not confused with “guaranteed approval.”

Google Play does not accept an MP4 upload. The preview field is a YouTube URL (public or unlisted, embeddable, monetization off). One master cut can go to App Store Connect as a file and to Play as a YouTube link.

What we shipped

/en/tools/app-preview stitches 3–8 PNG/JPG/WebP screenshots in the browser, optional captions and dissolves, clamps total length to 15–30 seconds, and exports 886×1920 · 30 fps · H.264 with a silent stereo AAC track (Apple expects a stereo layout). Encoding uses open-source mediabunny (MPL-2.0) + WebCodecs; nothing uploads. No stock music library—copyrighted audio is a common reason Play hides a preview behind ads.

We already covered preview vs screenshots, resolution specs, and product page header video. This piece is only the workflow: you already have store stills—how do you get a testable preview cut today?

Spec checklist

Play: upload the same MP4 to YouTube, paste a single video URL (not a playlist). Only the first ~30 seconds autoplay.

Steps: screenshots → MP4

1. Pick 3–6 UI proof frames from the stills you already designed for the listing—outcome first, then how it works. Skip empty states, pure settings, and poster-heavy creatives that belong on social, not in an App Preview.
2. Write one muted-safe caption per beat (about 3–6 words of benefit, not “All new”).
3. Open /en/tools/app-preview, upload in story order, set total length (try 20 seconds), enable short dissolves, export default 886×1920.
4. Watch the whole cut muted.
5. Split the upload path
   • App Store Connect → version → App Previews and Screenshots → drop the MP4 → set poster frame.
   • Play Console → YouTube first → paste the URL into the preview field; Feature Graphic remains the cover art.

If stills are the wrong size, fix them in batch export or the main screenshot generator before encoding—do not treat 1320×2868 still pixels as the video accepted size.

Slideshow vs device capture

Our bias: lock captions, order, and length on a slideshow first, then replace with device capture when you have time. A silent-clear 20s draft beats a polished 30s cut that never states the benefit.

Before you upload

• Length 15–30s; file well under 500MB
• Resolution is 886×1920 (or the accepted row for your target), not screenshot pixels
• Story works muted; no unauthorized music
• Subject is app UI, not hands-on-device B-roll
• Poster frame set (or you accept ~5s default)
• YouTube side: embeddable, not private, ads/monetization off

Captions and safe margins

Store pages often autoplay muted, so captions are the voiceover. Rules we use when exporting test cuts:

1. One line per beat, sized for a phone holding 886px-wide video—not for your laptop preview.
2. Keep type out of the Dynamic Island and home-indicator bands; this canvas is an accepted video size, not a framed marketing board.
3. No prices, flash sales, or ranking boasts—they age poorly and invite review friction.
4. Simple dots or arrows are fine to explain a tap; do not invent gestures the app lacks.

Still storyboarding? Lay five frames on Drawnix, export stills, then encode—cheaper than re-encoding every copy tweak.

When to use GIF instead

Keep folders separate (preview-886/, gif-demo/, header-21x9/) so you never upload the wrong file.

Size rejections → revisit the preview resolution guide. Deciding whether video is worth it → preview vs screenshot conversion.