# Mohammad Yehya

- **Event:** [Meta Global AI Developer Hackathon](https://cerebralvalley.ai/e/meta-ai-developer-hackathon)
- **When:** Oct 26, 12:00 PM – Nov 4, 9:00 PM (EST)
- **Where:** Online
- **Team:** [Mohammad Yehya](https://cerebralvalley.ai/u/mohammadyehya)
- **GitHub:** https://github.com/MohammadYehya/replay-board
- **Demo video:** https://youtu.be/WMNx1y5nFig
- **Gallery:** https://cerebralvalley.ai/e/meta-ai-developer-hackathon/hackathon/gallery
- **Page:** https://cerebralvalley.ai/e/meta-ai-developer-hackathon/hackathon/gallery/4973

Replay Board: rewatch a recorded lecture with a clean board beside it: the teacher's writing redrawn stroke by stroke, in sync with their voice, including what they hid while writing it.

THE PROBLEM
Recorded lectures are hard to rewatch. The teacher stands in front of what they are writing, the camera can't read the board, the cursor flies around the slides, and finding "where did she derive that?" means scrubbing through an hour of video. Students rewatch lectures to study, and the video is the worst possible format for that.

WHAT IT DOES
Upload a lecture video. Replay Board plays the original, untouched, next to a virtual board that redraws the writing stroke by stroke on the same clock as the video.
- Writing that was hidden behind the teacher appears anyway, at the moment it was talked about, with a small "was hidden" tag.
- Click any line to jump to where it was explained. Switch handwriting to typeset maths.
- Every word of the transcript is timed; chapters come from the lecture itself.
- When the teacher points at the board, the clean board shows it as a spotlight, circle, underline or arrow. On slide lectures, the restless cursor or laser becomes the same calm animations, on clean slides with the webcam blanked.
- Ask Muse: attach a formula from the first minute and a result from the last, ask how they connect, and get an answer whose times and board items you can click.
- 3D steps: a drawing opens in 3D, and the model changes step by step as the teacher explains it, each change at the word that names it, beside the video as it plays. "Try it" gives a slider per value.
- Slides export: the whole lecture as a deck that teaches it, with typeset formulas, worked steps, the teacher's own drawings and what was said in the speaker notes, downloaded as a real PowerPoint.

The original video is never altered: no outlining, blurring or removing the teacher.

HOW IT'S BUILT
Backend: Python, FastAPI, OpenCV, ffmpeg, torchaudio (MMS), python-pptx. Player: React, Vite, TypeScript, KaTeX and three.js. Board capture works on "writing stays put, the teacher moves": each pixel keeps counters that only move while the board is visible there, and camera drift of a pixel or two is tolerated. Self-tests on generated lectures with known answers score 136/136 on board lectures and 47/47 on slide lectures.

## More from Meta Global AI Developer Hackathon

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- [Timosgroup](https://cerebralvalley.ai/e/meta-ai-developer-hackathon/hackathon/gallery/4971)
- [Cobweb](https://cerebralvalley.ai/e/meta-ai-developer-hackathon/hackathon/gallery/4972)
- [Verify SI](https://cerebralvalley.ai/e/meta-ai-developer-hackathon/hackathon/gallery/4974)
- [Bevell](https://cerebralvalley.ai/e/meta-ai-developer-hackathon/hackathon/gallery/4975)
- [Sfaxo](https://cerebralvalley.ai/e/meta-ai-developer-hackathon/hackathon/gallery/4976)

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