Technical log of a local/offline player built with assisted AI: zero build step, portable atomic progress, and transcode fallback with Whisper subtitles in a P0–P3 queue.
3 parts · Updated Sep 19, 2026
How a local/offline player in Express + vanilla JS organizes thousands of lessons with no bundler: AGENTS.md as contract, physical structure as source of truth, and scan with on-disk cache.
How writeFileAtomic + serial queue + .bak + .corrupt-<ts> eliminated position loss even when killing the server mid-save.
Compatible files play directly via Range. Incompatible ones become fragmented MP4 with 416 seek. Subtitles are an add-on: never await before video.play().