How to make YouTube Shorts in 9:16 with Claude Code

ReelStyles · 16 October 2026

To make a YouTube Short with Claude Code, have it build a separate vertical film at 1080 × 1920 pixels instead of cropping your 16:9 video. Claude writes the scenes in HTML and JavaScript for the tall frame, a renderer like HyperFrames records them to MP4, and you check the size and the safe area before you upload. The same file works for Instagram Reels and TikTok.

This is how our own channels make their daily Shorts. Below are the steps, the measurements we use, and the styles we have tested in 9:16.

Why a separate film and not a crop

A 16:9 film cropped to 9:16 loses two thirds of the picture, and a 16:9 film shrunk into the middle of a tall frame leaves empty bands at the top and bottom. Both look like leftovers on a phone. A film composed for the tall frame uses all of it: things are stacked top to bottom (sky, faces, ground), the camera moves up and down, and one or two big faces replace the wide group shot.

You can still reuse the characters, sets and drawings from your long video. Only the shots are new.

Step 1: set the frame

Tell Claude the size up front:

Make a 35-second vertical film, 1080 x 1920, for YouTube Shorts.
It is a new film composed for the tall frame, not a crop of a 16:9 video.
Show me the shot list first.

If you use HyperFrames, the size lives in the composition's root element and its canvas. Ask Claude to keep them equal.

Step 2: keep text and faces in the safe area

Shorts, Reels and TikTok put their buttons, captions and channel name over your video. The rule our kits use: the platforms' interface covers about the top 250 pixels, the bottom 450 and the right 140. Keep all text, numbers and faces inside x 90 to 940 and y 250 to 1470. Let the background fill the whole frame edge to edge.

For text, use at least 44 pixels at 1080 wide, about four words per line, and one caption at a time.

Step 3: use a structure built for 30-odd seconds

A Short needs a different shape from a long video. One structure from our scan of YouTube outliers is the Then vs Now split Short: six split-screen comparisons of about four seconds each, small labels, music and sound effects with no voice, a reversal question at the end, and a last frame that matches the first so it loops. In the animated split montages we looked at, the 31 to 38 second ones did well and the 10 to 22 second ones did not.

Whatever structure you pick, put the first picture on screen in under a second.

Step 4: look at stills, then render

With HyperFrames:

npx hyperframes lint .
npx hyperframes snapshot . --at 1,3,5,7 -o snapshots
npx hyperframes render . -o out.mp4 --quality looks --workers 2

Look at the stills before you render. Check that no face or caption sits under the top or bottom band.

Step 5: check the file before you upload

Two quick checks with FFmpeg's tools:

ffprobe -v error -show_entries stream=width,height -of csv=p=0 out.mp4
ffmpeg -hide_banner -i out.mp4 -vf freezedetect=n=-50dB:d=1.2 -an -f null - 2>&1 | grep freeze_start

The first must print 1080,1920. The second prints nothing when no part of the film stands still for more than 1.2 seconds. A frozen stretch usually means a scene ended early or a shot has no motion.

Styles tested in 9:16

These 28 ReelStyles kits each have a vertical template and a vertical example film made by a fresh Claude Code given only the kit. The kits are plain files, so other agents such as Codex or Cursor can follow them too.

The other styles are tested in 16:9 only so far. You can still ask Claude for a vertical version of any of them, but you will be doing the framing work yourself.

A frame from the Round-head toon vertical example film

Sources

The safe-area numbers, checks and render steps are from the vertical render notes in our kits. The Short structure and its length figures are from our scan of 476 YouTube channels and 641 outlier videos (October 2026), listed on our formats page.

See all 72 styles and the price