The 4 NLP stages between raw YouTube subtitles and a flashcard you'd actually study

A lot of "learn English with YouTube" tools just dump every word from the captions into your face and call it a vocabulary list. The result is 80% noise — pronouns, articles, contractions, proper nouns, and the same 200 high-frequency words repeated until your brain melts. When I was building TubeVocab, the hardest engineering problem wasn't scraping subtitles or shipping the React UI. It was the linguistic plumbing between raw caption text and a card a B1 learner would actually benefit from stu