Developer Builds Cross-Device Workout App Using YouTube Timestamps as Training Units

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A developer building a personal fitness app called TrainFlow has shared the architectural decisions behind a system that treats YouTube video timestamps as reusable exercise objects rather than simple bookmarks. The design separates a full-featured desktop dashboard for planning routines from a focused mobile progressive web app for executing sessions. YouTube URLs are normalized at the point of entry into a validated data structure, extracting video IDs and converting timestamp formats into seconds for consistent use across the platform. Routines are built by referencing these timestamped actions rather than duplicating video metadata, keeping the data model lean and maintainable. The post, authored by TrainFlow's own maker, outlines engineering patterns used in the product built on Next.js App Router.

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