vincentsch/explainroo

Explainer videos made by your AI agent.
Free and open source. The voice, the timing and the rendering run on your computer.

Website  ·  Example videos  ·  Docs  ·  AGENTS.md

_{A coding agent made this video with explainroo. You can also watch it on explainroo.com.}

Copy this into your agent and put your topic in place of the brackets:

Make me a short explainer video about [your topic].
Use explainroo for it: clone https://github.com/vincentsch/explainroo,
read its AGENTS.md and follow the steps.

The agent sets up explainroo, makes the video and checks it. You get an MP4 file.

An explainer video is a short video where a voice explains a topic and drawings appear while it speaks. For explainroo, the agent writes two files. script.md has the words the voice says. scenes.js draws the pictures with a bit of JavaScript, and each drawing can appear on a word from the script. explainroo does the rest:

• Voice. Kokoro, an open voice model, reads the script aloud in English, Spanish, French, Italian, Brazilian Portuguese or Hindi. It has 41 voices and needs no account or API key. You can also use an ElevenLabs voice or record the narration yourself.
• Timing. Whisper listens to the narration and notes when each word is spoken.
• Pictures. Chrome runs in the background and draws the frames. The lines can look hand drawn (Rough.js), and there are 1,800 icons from Lucide. A scene can also show charts, math formulas, code that changes step by step, your own screenshots and video clips such as screen recordings.
• Sound. explainroo makes its own background music for each video and adds small sound effects. The music gets quieter while the voice speaks.
• File. ffmpeg puts it all together into an MP4, with subtitle files, YouTube chapters and a cover image.

An agent can't watch a video, so explainroo gives it other ways to check its work. It saves stills of the scenes and a sheet of small frames for the whole video. A layout check finds text that is cut off or overlaps, and a speech check finds words the voice got wrong. For a feed-sized player, explainroo check videos/<name> --view-width 854 also flags small text.

None of this leaves your computer, and it costs nothing. Your coding agent is a separate service with its own terms and prices. If you want, the agent can also make illustrations with an AI image model through OpenRouter, and you pay for each image.

There are six looks: paper, clean, chalk, blueprint, midnight and editorial. You change a video's look with one setting in video.json. A project can also bring its own look, a small JSON file with its colors, fonts and background. Here is one frame in each built-in look, from the example videos.

You pick the size for the place the video goes. YouTube videos are wide, and Shorts, TikTok and Reels are tall. Instagram and LinkedIn posts use 4:5, and there is a square size too. Shorts, TikTok and Reels put their own buttons over the video, and explainroo keeps your text out of those spots.

Tall, 4:5 and square videos get captions that light up word by word. One project can render several sizes: explainroo render videos/demo --size tiktok writes the TikTok version next to the wide one.

Every render also writes subtitle files (.srt and .vtt) that YouTube and LinkedIn accept, a cover image for the thumbnail, and YouTube chapters when the script names them. --format gif makes a GIF for a README or a post. --transparent --format mov makes a video with a transparent background, for putting a diagram over camera footage in a video editor. explainroo export writes a small web player that draws the video sharp at any size and embeds with an iframe.

"pace": 1.2 in a video's video.json makes the voice, the pauses and the animations 20% quicker. The music gets a little quicker too. Pace goes from 0.7 to 1.6, and 1 is normal.

explainroo can also make product demos, the videos software companies make to show their app. The agent rebuilds the app's screens from its code or its website, with the same colors, fonts and button labels. A mouse pointer then clicks through the screens and types into the fields. Tell your agent which product it is and where to find its code or website. explainroo capture saves the live site's screenshots, colors, fonts, logo and wording first, and a real screen recording can play inside a scene too.

Here are the demos for Unspar and Vroni, two of my own products. The files for the Unspar demo are in examples/unspar-demo. explainroo.com also has unofficial demos of Gmail, ChatGPT and Claude.

You need Node.js 20.11 or newer, ffmpeg, and Chrome or Chromium. The first setup downloads the voice and timing models once, about 400 MB together. You don't need a graphics card. I develop explainroo on Linux, and its tests run on Linux, macOS and Windows for every change.

git clone https://github.com/vincentsch/explainroo.git
cd explainroo
npm install
node bin/explainroo.js doctor --fetch

For narration in Spanish, French, Italian, Portuguese or Hindi, also install espeak-ng, for example with sudo apt install espeak-ng or brew install espeak-ng.

Then start your agent in the explainroo folder and ask for a video, for example "Make a 60 second video about how HTTPS keeps a password secret." The agent follows AGENTS.md and saves the video as videos/<name>/out/video.mp4. The example videos are in examples/, and the full documentation is on explainroo.com.

Each video has a small "explainroo.com" in one corner. "watermark": false in video.json turns it off. Please keep it if you can, because that is how other people find explainroo.

explainroo is MIT licensed. The voice comes from Kokoro, and the word timing from Whisper through Transformers.js. The drawings use Rough.js and Lucide icons. MathJax typesets the formulas. Playwright runs Chrome, and ffmpeg makes the video file. For other languages, explainroo runs espeak-ng as a separate program, with phoneme rules from Kokoro's misaki. The fonts are under the SIL Open Font License.