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How to render one video in wide and tall sizes at once with Explainroo

Make one project into a YouTube video and a TikTok or Reels version in one step.

  • Content
  • Intermediate
  • 45 minutes
  • From the README
  • Any agent

Who it is forA creator who posts the same explainer to YouTube, Shorts, TikTok and Instagram and wants each size without re-editing.

The problemEach platform needs a different frame size, and reformatting a finished video by hand loses captions and timing.

The outcomeSeparate renders of one project in wide, tall and square sizes, each with word-by-word captions where the size supports them.

What you need first

  • Node.js 20.11 or newer
  • ffmpeg
  • Chrome or Chromium
  • About 400 MB of disk space for the voice and timing models, downloaded once
  • A coding agent such as Claude Code or Codex, if you want the agent to write the video

Steps

  1. Set up Explainroo with npm install and node bin/explainroo.js doctor --fetch inside the repo folder
  2. Render the wide version and the tall version with explainroo render videos/demo --size tiktok
  3. Add "watermark": false to video.json only if you have a reason to remove the corner watermark
  4. Check small text for a phone screen with explainroo check videos/ --view-width 854
  5. Upload the MP4 with the .srt or .vtt subtitle file and the chapters the render writes

Prompt for your agent

In the explainroo repo at <repo folder>, render the project at videos/<project> in the wide size and the tiktok size. Expected output: two MP4 files next to each other. Verify that the tall version keeps your text clear of the platform buttons before you upload.

Caveat. The README says the watermark helps other people find Explainroo, and removing it with "watermark": false is up to you.

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