xgplayer is a production-grade, plugin-based HTML5 video player library maintained by ByteDance. It provides a core player package (`packages/xgplayer`) with UI controls, event/hook systems, device sniffing, i18n, and a rich plugin registry, plus separate npm packages for streaming protocols including HLS, FLV, DASH, MP4, and MPEG-TS transmuxing. The architecture is a monorepo of coordinated packages: streaming plugins built on shared networking, MSE, buffer, and error utilities; a custom type-level transmuxer that demuxes/remuxes FLV/TS/MP4 into fMP4 for Media Source Extensions; and extension packages for Chromecast/AirPlay, Google IMA ads, subtitles, and music visualization. In production this library plays both VOD and live streams in the browser, handles adaptive bitrate switching, DRM, low-latency manifest polling, and provides full control UI for desktop and mobile.