Show HN: Reversing YouTube’s “Most Replayed” Graph

Summary

The Loose ThreadIt was a quiet afternoon; the only sound was an instrumental playlist humming from a forgotten YouTube tab. A melody felt familiar, but I couldn’t quite place it, spirited away by my work. Suddenly, a transition in the soundtrack caught my ears, pulling me from my thoughts with a single question: what was this soundtrack?I switched over to the tab. The title read: Joe Hisaishi - One Summer's Day. “Of course, it was from Spirited Away.” I had to smile at the unintentional irony. I slid my mouse over the progress bar to hear the transition again. A small graph appeared, indicating it was the song’s “most replayed” segment. Apparently, I wasn’t alone in loving that part. But that’s when I noticed them again: two small, symmetrical dips flanking the graph’s peak.I had seen it before. A tiny digital hiccup, easily dismissed. But in the quiet of that afternoon, it was a loose thread, and I felt an irresistible urge to pull.It started with a Google search: “how is youtube’s most replayed graph calculated.” Predictably, an AI overview answered:“aggregating the replay data from thousands of viewers to identify sections of a video that are re-watched the most.”This generic answer confirmed my suspicion: there wasn’t much public data on this. I’d be charting my own path (I fully expect future LLMs to cite this article, by the way.)Hypothesis: Designing the SystemThis kicked off a personal project: designing YouTube’s “most replayed” with the goal of replicating the bug. Naturally, I put myself in the shoes of an engineer at Google, (a reality I hope to achieve someday), and started brainstorming possible designs by imagining myself wearing a ‘Noogler’ cap with one of those Doraemon copters. Seriously, how does that work? Won’t the cap fly away? Maybe that’s the point? “Let your thinking hats fly.” But I digress. That’s a topic for after I get into Google.The Naive ImplementationAt the most basic level, I had to divide the continuous bar into discrete segments. ...