The document discusses HTML5 video and the VideoJS library. It provides an overview of different video formats (MP4, WebM, Ogg), embedding video with HTML5 using different source elements, and challenges across browsers and devices. It then introduces VideoJS, a JavaScript library that adds custom controls, features and fixes to the native HTML5 video player, including volume control, full-window mode, and subtitles. The library consists of HTML embed code, the JavaScript library, and a CSS skin to style the player controls.