Reversing YouTube’s “Most Replayed” Graph
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Hi HN,I recently noticed a recurring visual artifact in the "Most Replayed" heatmap on the YouTube player. The highest peaks were always surrounded by two dips. I got curious about why they were there, so I decided to reverse engineer the feature to find out.This post documents the deep dive. It starts with a system design recreation, reverse engineering the rendering code, and ends with the mathematics.This is also my first attempt at writing an interactive article. I would love to hear your thoughts on the investigation and the format.
HN · launched Jan 16, 2026 · 87 upvotes (top 12%) · 0 views
Niche: video analytics and processing tools · 94 launches, 13 in the last 7 days ▲ +63% · Explore this niche →
Category and tags
- Media & entertainment
- Analytics & BI
- Developer
- Not AI
- Hobby / open-source project
Visit website ↗ Source listing ↗
More like this: all 94 launches in video analytics and processing tools →
Could you build this?
No This is a deep-dive reverse engineering research article exploring YouTube's internal signal processing, continuous smoothing algorithms, and mathematical representations of user heatmaps rather than a standalone vibe-codeable software product.
What it would actually take: Recreating or extracting the underlying math requires reverse-engineering obfuscated client-side video player code, mathematical analysis of cubic splines/smoothing filters, and decompilation of proprietary network protocols. It demands specialized knowledge in numerical analysis, reverse engineering, and video telemetry systems.
Discussion
20 comments analyzed.
Competitors mentioned: Josh Comeau's work (technical writing/documentation)
Concerns raised: Article is overly verbose and spends too much time on tangential details like the '100 segments' decision, Spline interpolation in YouTube creates misleading histogram visualization, YouTube bug with text field event handling persists since Windows 10
Feature requests: Variable time duration windows for histogram binning instead of fixed 100 segments, Fix YouTube's spline visualization to accurately represent underlying histogram data
Competitors
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Launched 77 days after the earliest competitor.
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