Lux is a fast and simple video downloader CLI tool written in Go. It supports downloading videos, images, and audio from over 40 websites including YouTube, Bilibili, TikTok, Instagram, Twitter, and many Chinese streaming platforms. The tool operates as a single binary with a rich set of command-line options for selecting quality, downloading playlists, resuming interrupted downloads, multi-threaded downloading, and integration with aria2 for RPC-based downloads. Architecturally, Lux follows a plugin-based extractor pattern. Each supported website has its own extractor module under `extractors/`, registered via `init()` functions into a global map keyed by domain. The main entry point is `main.go`, which parses CLI flags via `urfave/cli` and dispatches to the appropriate extractor. Extracted video metadata (streams, quality, size) is passed to the downloader, which handles HTTP requests, progress bars, file merging via ffmpeg, and optional subtitle embedding. Key data flows: URL input → domain detection → extractor selection → HTML/API scraping → stream metadata extraction → downloader (single or multi-threaded) → file output. External dependencies include ffmpeg for merging and subtitle embedding, and various third-party Go libraries for HTTP requests, HTML parsing, JavaScript execution (for TikTok signing), and progress bars. The codebase is well-organized with clear separation of concerns, extensive test coverage for individual extractors, and CI workflows that run weekly to verify extractor functionality. While many extractors rely on fragile regex-based scraping of HTML pages, the overall architecture is solid and the downloader implements robust features like resume support and configurable retry logic.